''Tyrannosaurus'' is a
genus
Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...
of large
theropod dinosaur
Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...
. The
species
In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...
''Tyrannosaurus rex'' (''rex'' meaning "king" in
Latin
Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...
), often called ''T. rex'' or colloquially ''T-Rex'', is one of the best represented theropods. ''Tyrannosaurus'' lived throughout what is now western
North America
North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...
, on what was then an island continent known as
Laramidia. ''Tyrannosaurus'' had a much wider range than other
tyrannosaurids
Tyrannosauridae (or tyrannosaurids, meaning "tyrant lizards") is a family (biology), family of coelurosaurian Theropoda, theropod dinosaurs that comprises two subfamilies containing up to thirteen genus, genera, including the eponymous ''Tyrannos ...
.
Fossil
A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...
s are found in a variety of
rock formations dating to the
Maastrichtian
The Maastrichtian () is, in the ICS geologic timescale, the latest age (uppermost stage) of the Late Cretaceous Epoch or Upper Cretaceous Series, the Cretaceous Period or System, and of the Mesozoic Era or Erathem. It spanned the interval from ...
age
Age or AGE may refer to:
Time and its effects
* Age, the amount of time someone or something has been alive or has existed
** East Asian age reckoning, an Asian system of marking age starting at 1
* Ageing or aging, the process of becoming older ...
of the Upper
Cretaceous
The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of th ...
period, 68 to 66
million years ago
The abbreviation Myr, "million years", is a unit of a quantity of (i.e. ) years, or 31.556926 teraseconds.
Usage
Myr (million years) is in common use in fields such as Earth science and cosmology. Myr is also used with Mya (million years ago). ...
. It was the last known member of the tyrannosaurids and among the last non-
avian
Avian may refer to:
*Birds or Aves, winged animals
*Avian (given name) (russian: Авиа́н, link=no), a male forename
Aviation
*Avro Avian, a series of light aircraft made by Avro in the 1920s and 1930s
*Avian Limited, a hang glider manufacture ...
dinosaurs to exist before the
Cretaceous–Paleogene extinction event
The Cretaceous–Paleogene (K–Pg) extinction event (also known as the Cretaceous–Tertiary extinction) was a sudden mass extinction of three-quarters of the plant and animal species on Earth, approximately 66 million years ago. With the ...
.
Like other tyrannosaurids, ''Tyrannosaurus'' was a
bipedal
carnivore with a massive skull balanced by a long, heavy tail. Relative to its large and powerful hind limbs, the forelimbs of ''Tyrannosaurus'' were short but unusually powerful for their size, and they had two clawed digits. The most complete specimen measures up to in length; however, according to most modern estimates, ''T. rex'' could grow to lengths of over , up to tall at the hips, and in body mass.
Although other theropods rivaled or exceeded ''Tyrannosaurus rex'' in
size
Size in general is the Magnitude (mathematics), magnitude or dimensions of a thing. More specifically, ''geometrical size'' (or ''spatial size'') can refer to linear dimensions (length, width, height, diameter, perimeter), area, or volume ...
, it is still among the largest known land predators and is estimated to have exerted the strongest bite force among all terrestrial animals. By far the largest carnivore in its environment, ''Tyrannosaurus rex'' was most likely an
apex predator, preying upon
hadrosaur
Hadrosaurids (), or duck-billed dinosaurs, are members of the ornithischian family Hadrosauridae. This group is known as the duck-billed dinosaurs for the flat duck-bill appearance of the bones in their snouts. The ornithopod family, which includ ...
s, juvenile armored herbivores like
ceratopsia
Ceratopsia or Ceratopia ( or ; Greek: "horned faces") is a group of herbivorous, beaked dinosaurs that thrived in what are now North America, Europe, and Asia, during the Cretaceous Period, although ancestral forms lived earlier, in the Jurassic. ...
ns and
ankylosaur
Ankylosauria is a group of herbivorous dinosaurs of the order Ornithischia. It includes the great majority of dinosaurs with armor in the form of bony osteoderms, similar to turtles. Ankylosaurs were bulky quadrupeds, with short, powerful limbs. ...
s, and possibly
sauropod
Sauropoda (), whose members are known as sauropods (; from '' sauro-'' + '' -pod'', 'lizard-footed'), is a clade of saurischian ('lizard-hipped') dinosaurs. Sauropods had very long necks, long tails, small heads (relative to the rest of their bo ...
s. Some experts have suggested the dinosaur was primarily a
scavenger
Scavengers are animals that consume dead organisms that have died from causes other than predation or have been killed by other predators. While scavenging generally refers to carnivores feeding on carrion, it is also a herbivorous feeding b ...
. The question of whether ''Tyrannosaurus'' was an apex predator or a pure scavenger was among the longest debates in
paleontology
Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (roughly 11,700 years before present). It includes the study of fossi ...
. Most paleontologists today accept that ''Tyrannosaurus'' was both an active predator and a scavenger.
Specimens of ''Tyrannosaurus rex'' include some that are nearly complete skeletons.
Soft tissue and
protein
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...
s have been reported in at least one of these specimens. The abundance of fossil material has allowed significant research into many aspects of its biology, including its life history and
biomechanics. The feeding habits,
physiology
Physiology (; ) is the scientific study of functions and mechanisms in a living system. As a sub-discipline of biology, physiology focuses on how organisms, organ systems, individual organs, cells, and biomolecules carry out the chemical ...
, and potential speed of ''Tyrannosaurus rex'' are a few subjects of debate. Its
taxonomy
Taxonomy is the practice and science of categorization or classification.
A taxonomy (or taxonomical classification) is a scheme of classification, especially a hierarchical classification, in which things are organized into groups or types. ...
is also controversial, as some scientists consider ''
Tarbosaurus bataar
''Tarbosaurus'' ( ; meaning "alarming lizard") is a genus of tyrannosaurid dinosaur that flourished in Asia about 70 million years ago, at the end of the Late Cretaceous Period, considered to contain a single known species, ''Tarbosaurus bataa ...
'' from Asia to be a second ''Tyrannosaurus'' species, while others maintain ''Tarbosaurus'' is a separate genus. Several other genera of North American tyrannosaurids have also been
synonymized with ''Tyrannosaurus''.
As the archetypal theropod, ''Tyrannosaurus'' has been one of the best-known dinosaurs since the early 20th century and has been featured in film, advertising, postal stamps, and many other media.
History of research
Earliest finds
![AMNH 3982 Manospondylus](https://upload.wikimedia.org/wikipedia/commons/b/b3/AMNH_3982_Manospondylus.jpg)
Teeth from what is now documented as a ''Tyrannosaurus rex'' were found in 1874 by
Arthur Lakes
Arthur Lakes (December 21, 1844—November 21, 1917) was an American geologist, artist, writer, teacher and Episcopalian minister. He captured much of his geological and palaeontological field work in sketches and watercolours. Lakes is credited ...
near
Golden, Colorado. In the early 1890s,
John Bell Hatcher collected postcranial elements in eastern
Wyoming
Wyoming () is a U.S. state, state in the Mountain states, Mountain West subregion of the Western United States. It is bordered by Montana to the north and northwest, South Dakota and Nebraska to the east, Idaho to the west, Utah to the south ...
. The fossils were believed to be from the large species ''
Ornithomimus grandis'' (now ''
Deinodon'') but are now considered ''T. rex'' remains.
In 1892,
Edward Drinker Cope
Edward Drinker Cope (July 28, 1840 – April 12, 1897) was an American zoologist, paleontologist, comparative anatomist, herpetologist, and ichthyologist. Born to a wealthy Quaker family, Cope distinguished himself as a child prodigy interested ...
found two vertebral fragments of a large dinosaur. Cope believed the fragments belonged to an "agathaumid" (
ceratopsid
Ceratopsidae (sometimes spelled Ceratopidae) is a family of ceratopsian dinosaurs including ''Triceratops'', ''Centrosaurus'', and ''Styracosaurus''. All known species were quadrupedal herbivores from the Upper Cretaceous. All but one species are k ...
) dinosaur, and named them ''Manospondylus gigas'', meaning "giant porous vertebra", in reference to the numerous openings for blood vessels he found in the bone.
The ''M. gigas'' remains were, in 1907, identified by Hatcher as those of a theropod rather than a ceratopsid.
Henry Fairfield Osborn recognized the similarity between ''Manospondylus gigas'' and ''T. rex'' as early as 1917, by which time the second vertebra had been lost. Owing to the fragmentary nature of the ''Manospondylus'' vertebrae, Osborn did not synonymize the two genera, instead considering the older genus indeterminate.
In June 2000, the
Black Hills Institute
The Black Hills Institute of Geological Research, Inc. (BHI) is a private corporation specializing in the excavation and preparation of fossils, as well as the sale of both original fossil material and museum-quality replicas. Founded in 1974 and b ...
found around 10% of a ''Tyrannosaurus'' skeleton (
BHI 6248) at a site that might have been the original ''M. gigas'' locality.
Skeleton discovery and naming
Barnum Brown
Barnum Brown (February 12, 1873 – February 5, 1963), commonly referred to as Mr. Bones, was an American paleontologist. Named after the circus showman P. T. Barnum, he discovered the first documented remains of ''Tyrannosaurus'' during a career ...
, assistant curator of the
American Museum of Natural History
The American Museum of Natural History (abbreviated as AMNH) is a natural history museum on the Upper West Side of Manhattan in New York City. In Theodore Roosevelt Park, across the street from Central Park, the museum complex comprises 26 inter ...
, found the first partial skeleton of ''T. rex'' in eastern Wyoming in 1900. Brown found another partial skeleton in the
Hell Creek Formation in Montana in 1902, comprising approximately 34 fossilized bones.
Writing at the time Brown said "Quarry No. 1 contains the femur, pubes, humerus, three vertebrae and two undetermined bones of a large Carnivorous Dinosaur not described by
Marsh
A marsh is a wetland that is dominated by herbaceous rather than woody plant species.Keddy, P.A. 2010. Wetland Ecology: Principles and Conservation (2nd edition). Cambridge University Press, Cambridge, UK. 497 p Marshes can often be found at ...
.... I have never seen anything like it from the
Cretaceous
The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of th ...
".
Henry Fairfield Osborn, president of the
American Museum of Natural History
The American Museum of Natural History (abbreviated as AMNH) is a natural history museum on the Upper West Side of Manhattan in New York City. In Theodore Roosevelt Park, across the street from Central Park, the museum complex comprises 26 inter ...
, named the second skeleton ''T. rex'' in 1905. The generic name is derived from the
Greek words ''τύραννος'' (''tyrannos'', meaning "tyrant") and ''
σαῦρος'' (''sauros'', meaning "lizard"). Osborn used the
Latin
Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...
word ''rex'', meaning "king", for the specific name. The full
binomial
Binomial may refer to:
In mathematics
*Binomial (polynomial), a polynomial with two terms
* Binomial coefficient, numbers appearing in the expansions of powers of binomials
*Binomial QMF, a perfect-reconstruction orthogonal wavelet decomposition
...
therefore translates to "tyrant lizard the king" or "King Tyrant Lizard", emphasizing the animal's size and perceived dominance over other species of the time.
![Dynamosaurus holotype](https://upload.wikimedia.org/wikipedia/commons/a/a2/Dynamosaurus_holotype.jpg)
Osborn named the other specimen ''Dynamosaurus imperiosus'' in a paper in 1905.
In 1906, Osborn recognized that the two skeletons were from the same species and selected ''Tyrannosaurus'' as the preferred name.
The original ''Dynamosaurus'' material resides in the collections of the
Natural History Museum, London.
In 1941, the ''T. rex'' type specimen was sold to the
Carnegie Museum of Natural History in Pittsburgh, Pennsylvania, for $7,000.
''Dynamosaurus'' would later be honored by the 2018 description of another species of tyrannosaurid by Andrew McDonald and colleagues, ''
Dynamoterror dynastes
''Dynamoterror'' (meaning "powerful terror") is a monospecific genus of tyrannosaurid dinosaur from New Mexico that lived during the Late Cretaceous (lower Campanian stage, 78 Ma) in what is now the upper Allison Member of the Menefee Formation. ...
'', whose name was chosen in reference to the 1905 name, as it had been a "childhood favorite" of McDonald's.
From the 1910s through the end of the 1950s, Barnum's discoveries remained the only specimens of ''Tyrannosaurus'', as the
Great Depression
The Great Depression (19291939) was an economic shock that impacted most countries across the world. It was a period of economic depression that became evident after a major fall in stock prices in the United States. The economic contagio ...
and wars kept many paleontologists out of the field.
Resurgent interest
![FMNH SUE Trex](https://upload.wikimedia.org/wikipedia/commons/8/82/FMNH_SUE_Trex.jpg)
Beginning in the 1960s, there was renewed interest in ''Tyrannosaurus'', resulting in the recovery of 42 skeletons (5–80% complete by bone count) from Western North America.
In 1967, Dr. William MacMannis located and recovered the skeleton named "MOR 008", which is 15% complete by bone count and has a reconstructed skull displayed at the
Museum of the Rockies
Museum of the Rockies is a museum in Bozeman, Montana. Originally affiliated with Montana State University in Bozeman, and now also, the Smithsonian Institution, the museum is largely known for its paleontological collections. The Museum houses ...
. The 1990s saw numerous discoveries, with nearly twice as many finds as in all previous years, including two of the most complete skeletons found to date:
Sue and
Stan
Stan or STAN may refer to:
People
* Stan (given name), a list of people with the given name
** Stan Laurel (1890–1965), English comic actor, part of duo Laurel and Hardy
* Stan (surname), a Romanian surname
* Stan! (born 1964), American author ...
.
Sue Hendrickson
Susan Hendrickson (born December 2, 1949) is an American explorer and fossil collector. Hendrickson is best known for her discovery of the remains of a ''Tyrannosaurus rex'' in South Dakota on August 12, 1990 in the Cheyenne River Reservation. H ...
, an
amateur
An amateur () is generally considered a person who pursues an avocation independent from their source of income. Amateurs and their pursuits are also described as popular, informal, autodidacticism, self-taught, user-generated, do it yourself, DI ...
paleontologist, discovered the most complete (approximately 85%) and largest ''Tyrannosaurus'' skeleton in the
Hell Creek Formation on August 12, 1990. The specimen Sue, named after the discoverer, was the object of a legal battle over its ownership. In 1997, the litigation was settled in favor of Maurice Williams, the original land owner. The fossil collection was purchased by the
Field Museum of Natural History
The Field Museum of Natural History (FMNH), also known as The Field Museum, is a natural history museum in Chicago, Illinois, and is one of the largest such museums in the world. The museum is popular for the size and quality of its educational ...
at auction for $7.6 million, making it the most expensive dinosaur skeleton until the sale of Stan for $31.8 million in 2020. From 1998 to 1999, Field Museum of Natural History staff spent over 25,000 hours taking the rock off the bones.
The bones were then shipped to
New Jersey
New Jersey is a state in the Mid-Atlantic and Northeastern regions of the United States. It is bordered on the north and east by the state of New York; on the east, southeast, and south by the Atlantic Ocean; on the west by the Delaware ...
where the mount was constructed, then shipped back to Chicago for the final assembly. The mounted skeleton opened to the public on May 17, 2000, in the Field Museum of Natural History. A study of this specimen's fossilized bones showed that Sue reached full size at age 19 and died at the age of 28, the longest estimated life of any tyrannosaur known.
![Scotty Tyrannosaurus](https://upload.wikimedia.org/wikipedia/commons/a/a7/Scotty_Tyrannosaurus.jpg)
Another ''Tyrannosaurus'', nicknamed Stan (BHI 3033), in honor of amateur paleontologist Stan Sacrison, was recovered from the Hell Creek Formation in 1992. Stan is the second most complete skeleton found, with 199 bones recovered representing 70% of the total. This tyrannosaur also had many bone pathologies, including broken and healed ribs, a broken (and healed) neck, and a substantial hole in the back of its head, about the size of a ''Tyrannosaurus'' tooth.
In 1998, Bucky Derflinger noticed a ''T. rex'' toe exposed above ground, making Derflinger, who was 20 years old at the time, the youngest person to discover a ''Tyrannosaurus''. The specimen, dubbed
Bucky in honor of its discoverer, was a young adult, tall and long. Bucky is the first ''Tyrannosaurus'' to be found that preserved a
furcula (wishbone). Bucky is permanently displayed at
The Children's Museum of Indianapolis.
![Tyrannosaurus specimens](https://upload.wikimedia.org/wikipedia/commons/c/c3/Tyrannosaurus_specimens.svg)
In the summer of 2000, crews organized by
Jack Horner Jack Horner may refer to:
*''Little Jack Horner'', a nursery rhyme
People
* Jack Horner (baseball) (1863–1910), American professional baseball player
*Jack Horner (journalist) (1912–2005), Gordon John Horner, Minnesota sportscaster
* Jack B. H ...
discovered five ''Tyrannosaurus'' skeletons near the
Fort Peck Reservoir
The Fort Peck Dam is the highest of six major dams along the Missouri River, located in northeast Montana in the United States, near Glasgow, and adjacent to the community of Fort Peck. At in length and over in height, it is the largest hyd ...
.
In 2001, a 50% complete skeleton of a juvenile ''Tyrannosaurus'' was discovered in the Hell Creek Formation by a crew from the
Burpee Museum of Natural History
The Burpee Museum of Natural History is located along the Rock River in downtown Rockford, Illinois, United States, at 737 North Main Street.
Museum history
The museum was created as a Works Progress Administration project. It was established ...
. Dubbed Jane (BMRP 2002.4.1), the find was thought to be the first known skeleton of a
pygmy tyrannosaurid, ''
Nanotyrannus
''Tyrannosaurus'' is a genus of large theropod dinosaur. The species ''Tyrannosaurus rex'' (''rex'' meaning "king" in Latin), often called ''T. rex'' or colloquially ''T-Rex'', is one of the best represented theropods. ''Tyrannosaurus'' live ...
'', but subsequent research revealed that it is more likely a juvenile ''Tyrannosaurus'', and the most complete juvenile example known;
Jane is exhibited at the Burpee Museum of Natural History. In 2002, a skeleton named Wyrex, discovered by amateur collectors Dan Wells and Don Wyrick, had 114 bones and was 38% complete. The dig was concluded over 3 weeks in 2004 by the
Black Hills Institute
The Black Hills Institute of Geological Research, Inc. (BHI) is a private corporation specializing in the excavation and preparation of fossils, as well as the sale of both original fossil material and museum-quality replicas. Founded in 1974 and b ...
with the first live
online
In computer technology and telecommunications, online indicates a state of connectivity and offline indicates a disconnected state. In modern terminology, this usually refers to an Internet connection, but (especially when expressed "on line" or ...
''Tyrannosaurus'' excavation providing daily reports, photos, and video.
In 2006,
Montana State University
Montana State University (MSU) is a Public university, public land-grant university, land-grant research university in Bozeman, Montana. It is the state's largest university. MSU offers baccalaureate degrees in 60 fields, master's degrees in 6 ...
revealed that it possessed the largest ''Tyrannosaurus'' skull yet discovered (from a specimen named MOR 008), measuring long.
Subsequent comparisons indicated that the longest head was (from specimen LACM 23844) and the widest head was (from Sue).
Footprints
![Philmont Scout Ranch Tyrannosaurus footprint](https://upload.wikimedia.org/wikipedia/commons/a/af/Philmont_Scout_Ranch_Tyrannosaurus_footprint.jpg)
Two isolated fossilized
footprints have been tentatively assigned to ''T. rex''. The first was discovered at
Philmont Scout Ranch
Philmont Scout Ranch is a ranch located in Colfax County, New Mexico, near the village of Cimarron; it covers of wilderness in the Sangre de Cristo Mountains on the east side of the Cimarron Range of the Rocky Mountains. Donated by oil baro ...
, New Mexico, in 1983 by American geologist Charles Pillmore. Originally thought to belong to a
hadrosaurid
Hadrosaurids (), or duck-billed dinosaurs, are members of the ornithischian family Hadrosauridae. This group is known as the duck-billed dinosaurs for the flat duck-bill appearance of the bones in their snouts. The ornithopod family, which inclu ...
, examination of the footprint revealed a large 'heel' unknown in
ornithopod
Ornithopoda () is a clade of ornithischian dinosaurs, called ornithopods (), that started out as small, bipedal running grazers and grew in size and numbers until they became one of the most successful groups of herbivores in the Cretaceous world ...
dinosaur tracks, and traces of what may have been a
hallux
Toes are the digits (fingers) of the foot of a tetrapod. Animal species such as cats that walk on their toes are described as being '' digitigrade''. Humans, and other animals that walk on the soles of their feet, are described as being '' pl ...
, the dewclaw-like fourth digit of the tyrannosaur foot. The footprint was published as the
ichnogenus ''
Tyrannosauripus pillmorei'' in 1994, by
Martin Lockley
Martin G. Lockley (born 1950) is a Welsh palaeontologist. He was educated in the United Kingdom where he obtained degrees (BSc and PhD) and post-doctoral experience in Geology in the 1970s. Since 1980 he has been a professor at the Universit ...
and Adrian Hunt. Lockley and Hunt suggested that it was very likely the track was made by a ''T. rex'', which would make it the first known footprint from this species. The track was made in what was once a vegetated wetland mudflat. It measures long by wide.
A second footprint that may have been made by a ''Tyrannosaurus'' was first reported in 2007 by British paleontologist Phil Manning, from the
Hell Creek Formation of Montana. This second track measures long, shorter than the track described by Lockley and Hunt. Whether or not the track was made by ''Tyrannosaurus'' is unclear, though ''Tyrannosaurus'' is the only large theropod known to have existed in the Hell Creek Formation.
A set of footprints in Glenrock, Wyoming dating to the
Maastrichtian
The Maastrichtian () is, in the ICS geologic timescale, the latest age (uppermost stage) of the Late Cretaceous Epoch or Upper Cretaceous Series, the Cretaceous Period or System, and of the Mesozoic Era or Erathem. It spanned the interval from ...
stage of the Late Cretaceous and hailing from the
Lance Formation were described by Scott Persons, Phil Currie and colleagues in 2016, and are believed to belong to either a juvenile ''T. rex'' or the dubious tyrannosaurid ''Nanotyrannus lancensis''. From measurements and based on the positions of the footprints, the animal was believed to be traveling at a walking speed of around 2.8 to 5 miles per hour and was estimated to have a hip height of to . A follow-up paper appeared in 2017, increasing the speed estimations by 50–80%.
Description
Size
![Longest theropods](https://upload.wikimedia.org/wikipedia/commons/a/af/Longest_theropods.svg)
''T. rex'' was one of the largest land carnivores of all time. One of the largest and the most complete specimens, nicknamed
Sue (FMNH PR2081), is located at the
Field Museum of Natural History
The Field Museum of Natural History (FMNH), also known as The Field Museum, is a natural history museum in Chicago, Illinois, and is one of the largest such museums in the world. The museum is popular for the size and quality of its educational ...
in Chicago. Sue measured long,
was tall at the hips,
and according to the most recent studies, using a variety of techniques, maximum body masses have been estimated approximately .
A specimen nicknamed
Scotty (RSM P2523.8), located at the
Royal Saskatchewan Museum, is reported to measure in length. Using a mass estimation technique that extrapolates from the
circumference
In geometry, the circumference (from Latin ''circumferens'', meaning "carrying around") is the perimeter of a circle or ellipse. That is, the circumference would be the arc length of the circle, as if it were opened up and straightened out to ...
of the femur, Scotty was estimated as the largest known specimen at in body mass.
Not every adult ''Tyrannosaurus'' specimen recovered is as big. Historically average adult mass estimates have varied widely over the years, from as low as ,
to more than ,
with most modern estimates ranging between and .
Skull
![Tyrannoskull](https://upload.wikimedia.org/wikipedia/commons/e/e4/Tyrannoskull.jpg)
The largest known ''T. rex'' skulls measure up to in length.
Large
fenestrae
A fenestra (fenestration; plural fenestrae or fenestrations) is any small opening or pore, commonly used as a term in the biological sciences. It is the Latin word for "window", and is used in various fields to describe a pore in an anatomical st ...
(openings) in the skull reduced weight, as in all carnivorous theropods. In other respects ''Tyrannosaurus''
's skull was significantly different from those of large non-
tyrannosaurid
Tyrannosauridae (or tyrannosaurids, meaning "tyrant lizards") is a family of coelurosaurian theropod dinosaurs that comprises two subfamilies containing up to thirteen genera, including the eponymous ''Tyrannosaurus''. The exact number of genera ...
theropods. It was extremely wide at the rear but had a narrow snout, allowing unusually good
binocular vision.
The skull bones were massive and the
nasals and some other bones were fused, preventing movement between them; but many were
pneumatized (contained a "honeycomb" of tiny air spaces) and thus lighter. These and other skull-strengthening features are part of the
tyrannosaurid
Tyrannosauridae (or tyrannosaurids, meaning "tyrant lizards") is a family of coelurosaurian theropod dinosaurs that comprises two subfamilies containing up to thirteen genera, including the eponymous ''Tyrannosaurus''. The exact number of genera ...
trend towards an increasingly powerful bite, which easily surpassed that of all non-tyrannosaurids.
The tip of the upper jaw was U-shaped (most non-tyrannosauroid carnivores had V-shaped upper jaws), which increased the amount of tissue and bone a tyrannosaur could rip out with one bite, although it also increased the stresses on the front teeth.
The teeth of ''T. rex'' displayed marked
heterodont
In anatomy, a heterodont (from Greek, meaning 'different teeth') is an animal which possesses more than a single tooth morphology.
In vertebrates, heterodont pertains to animals where teeth are differentiated into different forms. For example, ...
y (differences in shape).
The
premaxilla
The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammal has b ...
ry teeth, four per side at the front of the upper jaw, were closely packed, ''D''-shaped in cross-section, had reinforcing ridges on the rear surface, were
incisiform (their tips were chisel-like blades) and curved backwards. The ''D''-shaped cross-section, reinforcing ridges and backwards curve reduced the risk that the teeth would snap when ''Tyrannosaurus'' bit and pulled. The remaining teeth were robust, like "lethal bananas" rather than daggers, more widely spaced and also had reinforcing ridges.
Those in the upper jaw, twelve per side in mature individuals,
were larger than their counterparts of the lower jaw, except at the rear. The largest found so far is estimated to have been long including the root when the animal was alive, making it the largest tooth of any carnivorous dinosaur yet found.
The lower jaw was robust. Its front
dentary bone
In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower teeth in place. The mandible sits beneath the maxilla. It is the only movable bone ...
bore thirteen teeth. Behind the tooth row, the lower jaw became notably taller.
The upper and lower jaws of ''Tyrannosaurus'', like those of many dinosaurs, possessed numerous
foramina, or small holes in the bone. Various functions have been proposed for these foramina, such as a crocodile-like sensory system
or evidence of
extra-oral structures such as scales or potentially lips.
Skeleton
The
vertebral column
The vertebral column, also known as the backbone or spine, is part of the axial skeleton. The vertebral column is the defining characteristic of a vertebrate in which the notochord (a flexible rod of uniform composition) found in all chordata, ...
of ''Tyrannosaurus'' consisted of ten neck vertebrae, thirteen back vertebrae and five sacral vertebrae. The number of tail vertebrae is unknown and could well have varied between individuals but probably numbered at least forty. Sue was mounted with forty-seven of such caudal vertebrae.
The neck of ''T. rex'' formed a natural S-shaped curve like that of other theropods. Compared to these, it was exceptionally short, deep and muscular to support the massive head. The second vertebra, the axis, was especially short. The remaining neck vertebrae were weakly opisthocoelous, i.e. with a convex front of the vertebral body and a concave rear. The vertebral bodies had single pleurocoels, pneumatic depressions created by
air sac
Air sacs are spaces within an organism where there is the constant presence of air. Among modern animals, birds possess the most air sacs (9–11), with their extinct dinosaurian relatives showing a great increase in the pneumatization (presence ...
s, on their sides.
The vertebral bodies of the torso were robust but with a narrow waist. Their undersides were keeled. The front sides were concave with a deep vertical trough. They had large pleurocoels. Their neural spines had very rough front and rear sides for the attachment of strong tendons. The sacral vertebrae were fused to each other, both in their vertebral bodies and neural spines. They were pneumatized. They were connected to the pelvis by transverse processes and sacral ribs. The tail was heavy and moderately long, in order to balance the massive head and torso and to provide space for massive
locomotor muscles that attached to the thighbones. The thirteenth tail vertebra formed the transition point between the deep tail base and the middle tail that was stiffened by a rather long front articulation processes. The underside of the trunk was covered by eighteen or nineteen pairs of segmented belly ribs.
![The Right Arm of SUE](https://upload.wikimedia.org/wikipedia/commons/2/21/The_Right_Arm_of_SUE.jpg)
The
shoulder girdle
The shoulder girdle or pectoral girdle is the set of bones in the appendicular skeleton which connects to the arm on each side. In humans it consists of the clavicle and scapula; in those species with three bones in the shoulder, it consists of t ...
was longer than the entire forelimb. The shoulder blade had a narrow shaft but was exceptionally expanded at its upper end. It connected via a long forward protrusion to the
coracoid, which was rounded. Both shoulder blades were connected by a small
furcula. The paired breast bones possibly were made of
cartilage
Cartilage is a resilient and smooth type of connective tissue. In tetrapods, it covers and protects the ends of long bones at the joints as articular cartilage, and is a structural component of many body parts including the rib cage, the neck an ...
only.
The forelimb or arm was very short. The upper arm bone, the humerus, was short but robust. It had a narrow upper end with an exceptionally rounded head. The lower arm bones, the
ulna
The ulna (''pl''. ulnae or ulnas) is a long bone found in the forearm that stretches from the elbow to the smallest finger, and when in anatomical position, is found on the medial side of the forearm. That is, the ulna is on the same side of t ...
and radius, were straight elements, much shorter than the humerus. The second
metacarpal was longer and wider than the first, whereas normally in theropods the opposite is true. The forelimbs had only two clawed fingers,
along with an additional splint-like small third
metacarpal representing the remnant of a third digit.
![UCMP Trex pelvis 2](https://upload.wikimedia.org/wikipedia/commons/6/6d/UCMP_Trex_pelvis_2.JPG)
The
pelvis
The pelvis (plural pelves or pelvises) is the lower part of the trunk, between the abdomen and the thighs (sometimes also called pelvic region), together with its embedded skeleton (sometimes also called bony pelvis, or pelvic skeleton).
The ...
was a large structure. Its upper bone, the
ilium, was both very long and high, providing an extensive attachment area for hindlimb muscles. The front
pubic bone ended in an enormous pubic boot, longer than the entire shaft of the element. The rear
was slender and straight, pointing obliquely to behind and below.
In contrast to the arms, the hindlimbs were among the longest in proportion to body size of any theropod. In the foot, the
metatarsus was "arctometatarsalian", meaning that the part of the third metatarsal near the ankle was pinched. The third metatarsal was also exceptionally sinuous.
Compensating for the immense bulk of the animal, many bones throughout the skeleton were hollowed, reducing its weight without significant loss of strength.
Classification
![Tyrannosaurus skulls Japan](https://upload.wikimedia.org/wikipedia/commons/4/47/Tyrannosaurus_skulls_Japan.jpg)
''Tyrannosaurus'' is the
type genus of the superfamily
Tyrannosauroidea
Tyrannosauroidea (meaning 'tyrant lizard forms') is a superfamily (or clade) of coelurosaurian theropod dinosaurs that includes the family Tyrannosauridae as well as more basal relatives. Tyrannosauroids lived on the Laurasian supercontinent b ...
, the
family
Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...
Tyrannosauridae, and the subfamily Tyrannosaurinae; in other words it is the standard by which paleontologists decide whether to include other species in the same group. Other members of the tyrannosaurine subfamily include the North American ''
Daspletosaurus
''Daspletosaurus'' ( ; meaning "frightful lizard") is a genus of tyrannosaurid dinosaur that lived in Laramidia between about 79.5 and 74 million years ago, during the Late Cretaceous Period. The genus ''Daspletosaurus'' contains three species ...
'' and the
Asia
Asia (, ) is one of the world's most notable geographical regions, which is either considered a continent in its own right or a subcontinent of Eurasia, which shares the continental landmass of Afro-Eurasia with Africa. Asia covers an area ...
n ''
Tarbosaurus'',
both of which have occasionally been synonymized with ''Tyrannosaurus''.
Tyrannosaurids were once commonly thought to be descendants of earlier large theropods such as
megalosaurs
Megalosauroidea (meaning 'great/big lizard forms') is a Taxonomic rank, superfamily (or clade) of Tetanurae, tetanuran theropod dinosaurs that lived from the Middle Jurassic to the Late Cretaceous period. The group is defined as ''Megalosaurus, M ...
and
carnosaurs, although more recently they were reclassified with the generally smaller
coelurosaurs
Coelurosauria (; from Greek, meaning "hollow tailed lizards") is the clade containing all theropod dinosaurs more closely related to birds than to carnosaurs.
Coelurosauria is a subgroup of theropod dinosaurs that includes compsognathids, tyrann ...
.
Many
phylogenetic
In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...
analyses have found ''
Tarbosaurus bataar
''Tarbosaurus'' ( ; meaning "alarming lizard") is a genus of tyrannosaurid dinosaur that flourished in Asia about 70 million years ago, at the end of the Late Cretaceous Period, considered to contain a single known species, ''Tarbosaurus bataa ...
'' to be the
sister taxon
In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree.
Definition
The expression is most easily illustrated by a cladogram:
Taxon A and t ...
of ''T. rex''.
The discovery of the tyrannosaurid ''
Lythronax
''Lythronax'' () is a genus of tyrannosaurid dinosaur that lived in North America around 81.9-81.5 million years ago during the Late Cretaceous period. The only known specimen was discovered in Utah in the Wahweap Formation of the Grand Stairca ...
'' further indicates that ''Tarbosaurus'' and ''Tyrannosaurus'' are closely related, forming a clade with fellow Asian tyrannosaurid ''
Zhuchengtyrannus'', with ''Lythronax'' being their sister taxon.
A further study from 2016 by Steve Brusatte, Thomas Carr and colleagues, also indicates that ''Tyrannosaurus'' may have been an immigrant from Asia, as well as a possible descendant of ''Tarbosaurus''.
Below is the cladogram of Tyrannosauridae based on the
phylogenetic analysis conducted by Loewen and colleagues in 2013.
Additional species
![Tarbosaurus and Tyrannosaurus](https://upload.wikimedia.org/wikipedia/commons/9/96/Tarbosaurus_and_Tyrannosaurus.jpg)
In 1955, Soviet
paleontologist
Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (roughly 11,700 years before present). It includes the study of fossi ...
Evgeny Maleev
Evgeny Aleksandrovich Maleev (, ; 25 February 1915 – 12 April 1966) was a Soviet and Russian paleontologist who did most of his research on reptiles and Asian fossils, such as the naming of the ankylosaur ''Talarurus'' and theropods ''Tarbo ...
named a new species, ''Tyrannosaurus bataar'', from
Mongolia
Mongolia; Mongolian script: , , ; lit. "Mongol Nation" or "State of Mongolia" () is a landlocked country in East Asia, bordered by Russia to the north and China to the south. It covers an area of , with a population of just 3.3 million, ...
.
By 1965, this species was renamed as a distinct genus, ''Tarbosaurus bataar''.
While most palaeontologists continue to maintain the two as distinct genera, some authors such as
Thomas Holtz
Thomas Richard Holtz Jr. (born September 13, 1965) is an American vertebrate palaeontologist, author, and principal lecturer at the University of Maryland's Department of Geology. He has published extensively on the phylogeny, morphology, ecomorp ...
,
Kenneth Carpenter, and
Thomas Carr argue that the two species are similar enough to be considered members of the same genus, with the Mongolian
taxon
In biology, a taxon (back-formation from ''taxonomy''; plural taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular nam ...
having the resulting
binomial
Binomial may refer to:
In mathematics
*Binomial (polynomial), a polynomial with two terms
* Binomial coefficient, numbers appearing in the expansions of powers of binomials
*Binomial QMF, a perfect-reconstruction orthogonal wavelet decomposition
...
of ''Tyrannosaurus bataar''.
[
In 2001, various tyrannosaurid teeth and a metatarsal unearthed in a quarry near Zhucheng, China were assigned by Chinese paleontologist ]Hu Chengzhi
Hu Chengzhi (; 23 August 1917 – 12 April 2018) was a Chinese paleontologist and paleoanthropologist. He made the plaster casts of the Peking Man skull in the 1930s, and identified the Yuanmou Man (''Homo erectus yuanmouensis'') based on fossil ...
to the newly erected species ''Tyrannosaurus zhuchengensis''. However, in a nearby site, a right maxilla and left jawbone were assigned to the newly erected tyrannosaurid genus ''Zhuchengtyrannus'' in 2011. It is possible that ''T. zhuchengensis'' is synonymous
A synonym is a word, morpheme, or phrase that means exactly or nearly the same as another word, morpheme, or phrase in a given language. For example, in the English language, the words ''begin'', ''start'', ''commence'', and ''initiate'' are all ...
with ''Zhuchengtyrannus''. In any case, ''T. zhuchengensis'' is considered to be a ''nomen dubium
In binomial nomenclature, a ''nomen dubium'' (Latin for "doubtful name", plural ''nomina dubia'') is a scientific name that is of unknown or doubtful application.
Zoology
In case of a ''nomen dubium'' it may be impossible to determine whether a s ...
'' as the holotype lacks diagnostic
Diagnosis is the identification of the nature and cause of a certain phenomenon. Diagnosis is used in many different disciplines, with variations in the use of logic, analytics, and experience, to determine " cause and effect". In systems engine ...
features below the level Tyrannosaurinae.
In a 2022 study, Gregory S. Paul and colleagues argued that ''Tyrannosaurus rex'', as traditionally understood, actually represents three species: the type species ''Tyrannosaurus rex'', and two new species: ''T. imperator'' (meaning "tyrant lizard emperor") and ''T. regina'' (meaning "tyrant lizard queen"). The holotype of the former (''T. imperator'') is the Sue specimen, and the holotype of the latter (''T. regina'') is Wankel rex
''Tyrannosaurus'' is one of the most iconic dinosaurs and is known from numerous specimens, some of which have individually acquired notability due to their scientific significance and media coverage.
Specimen data
''Manospondylus'': AMNH 39 ...
. The division into multiple species was primarily based on the observation of a very high degree of variation in the proportions and robusticity of the femur
The femur (; ), or thigh bone, is the proximal bone of the hindlimb in tetrapod vertebrates. The head of the femur articulates with the acetabulum in the pelvic bone forming the hip joint, while the distal part of the femur articulates with ...
(and other skeletal elements) across catalogued ''T. rex'' specimens, more so than that observed in other theropods recognized as one species. Differences of general body proportions representing robust and gracile morphotypes was also used as a line of evidence, in addition to the number of small, slender incisiform teeth in the dentary, as based on tooth sockets. Specifically, the paper's ''T. rex'' was distinguished by robust anatomy, a moderate ratio of femur length vs circumference, and the possession of a singular slender incisiform dentary tooth; ''T. imperator'' was considered to be robust with a small femur length to circumference ratio and two of the slender teeth; and ''T. regina'' was a gracile form with a high femur ratio and one of the slender teeth. It was observed that variation in proportions and robustness became more extreme higher up in the sample, stratigraphically
Stratigraphy is a branch of geology concerned with the study of rock layers (strata) and layering (stratification). It is primarily used in the study of sedimentary and layered volcanic rocks.
Stratigraphy has three related subfields: lithostrati ...
. This was interpreted as a single earlier population, ''T. imperator'', speciating into more than one taxon, ''T. rex'' and ''T. regina''.
However, several other leading paleontologists, including Stephen Brusatte, Thomas Carr, Thomas Holtz
Thomas Richard Holtz Jr. (born September 13, 1965) is an American vertebrate palaeontologist, author, and principal lecturer at the University of Maryland's Department of Geology. He has published extensively on the phylogeny, morphology, ecomorp ...
, David Hone, Jingmai O'Connor
Jingmai Kathleen O'Connor (; born August 26, 1983) is a paleontologist who works as a curator at the Field Museum.
Biography
O'Connor is from Pasadena, California. Her mother is a geologist. O'Connor says that while she was not a dinosaur enthu ...
, and Lindsay Zanno, criticized the study or expressed skepticism of its conclusions when approached by various media outlets for comment. Their criticism was subsequently published in a technical paper.[Carr T.D., Napoli J.G., Brusatte S.L., Holtz T.R., Hone D.W.E., Williamson T.E. & Zanno L.E. (2022). “Insufficient Evidence for Multiple Species of Tyrannosaurus in the Latest Cretaceous of North America: A Comment on “The Tyrant Lizard King, Queen and Emperor: Multiple Lines of Morphological and Stratigraphic Evidence Support Subtle Evolution and Probable Speciation Within the North American Genus Tyrannosaurus””. ''Evolutionary Biology'' 49(3): p. 314-341: doi.org/10.1007/s11692-022-09573-1] Holtz and Zanno both remarked that it was plausible that more than one species of ''Tyrannosaurus'' existed, but felt the new study was insufficient to support the species it proposed. Holtz remarked that, even if ''Tyrannosaurus imperator'' represented a distinct species from ''Tyrannosaurus rex'', it may represent the same species as ''Nanotyrannus lancensis'' and would need to be called ''Tyrannosaurus lancensis''. O'Connor, a curator at the Field Museum, where the ''T. imperator'' holotype Sue is displayed, regarded the new species as too poorly-supported to justify modifying the exhibit signs. Brusatte, Carr, and O'Connor viewed the distinguishing features proposed between the species as reflecting natural variation within a species. Both Carr and O'Connor expressed concerns about the study's inability to determine which of the proposed species several well-preserved specimens belonged to. Another paleontologist, Philip J. Currie
Philip John Currie (born March 13, 1949) is a Canadian palaeontologist and museum curator who helped found the Royal Tyrrell Museum of Palaeontology in Drumheller, Alberta and is now a professor at the University of Alberta in Edmonton. In the ...
, originally co-authored the study but withdrew from it as he did not want to be involved in naming the new species.
''Nanotyrannus''
Other tyrannosaurid fossils found in the same formations as ''T. rex'' were originally classified as separate taxa, including ''Aublysodon'' and ''Albertosaurus megagracilis'', the latter being named ''Dinotyrannus megagracilis'' in 1995. These fossils are now universally considered to belong to juvenile ''T. rex''. A small but nearly complete skull from Montana, long, might be an exception. This skull, CMNH 7541, was originally classified as a species of '' Gorgosaurus'' (''G. lancensis'') by Charles W. Gilmore
Charles Whitney Gilmore (March 11, 1874 – September 27, 1945) was an American paleontologist who gained renown in the early 20th century for his work on vertebrate fossils during his career at the United States National Museum (now the N ...
in 1946. In 1988, the specimen was re-described by Robert T. Bakker
Robert Thomas Bakker (born March 24, 1945) is an American paleontologist who helped reshape modern theories about dinosaurs, particularly by adding support to the theory that some dinosaurs were endothermic (warm-blooded). Along with his mentor J ...
, Phil Currie, and Michael Williams, then the curator of paleontology at the Cleveland Museum of Natural History, where the original specimen was housed and is now on display. Their initial research indicated that the skull bones were fused, and that it therefore represented an adult specimen. In light of this, Bakker and colleagues assigned the skull to a new genus named ''Nanotyrannus'' (meaning "dwarf tyrant", for its apparently small adult size). The specimen is estimated to have been around long when it died. However, In 1999, a detailed analysis by Thomas Carr revealed the specimen to be a juvenile, leading Carr and many other paleontologists to consider it a juvenile ''T. rex'' individual.
In 2001, a more complete juvenile tyrannosaur (nicknamed "Jane
Jane may refer to:
* Jane (given name), a feminine given name
* Jane (surname), related to the given name
Film and television
* ''Jane'' (1915 film), a silent comedy film directed by Frank Lloyd
* ''Jane'' (2016 film), a South Korean drama fil ...
", catalog number BMRP 2002.4.1), belonging to the same species as the original ''Nanotyrannus'' specimen, was uncovered. This discovery prompted a conference on tyrannosaurs focused on the issues of ''Nanotyrannus'' validity at the Burpee Museum of Natural History
The Burpee Museum of Natural History is located along the Rock River in downtown Rockford, Illinois, United States, at 737 North Main Street.
Museum history
The museum was created as a Works Progress Administration project. It was established ...
in 2005. Several paleontologists who had previously published opinions that ''N. lancensis'' was a valid species, including Currie and Williams, saw the discovery of "Jane" as a confirmation that ''Nanotyrannus'' was, in fact, a juvenile ''T. rex''.[Currie, Henderson, Horner and Williams (2005). "On tyrannosaur teeth, tooth positions and the taxonomic status of ''Nanotyrannus lancensis''." In "The origin, systematics, and paleobiology of Tyrannosauridae", a symposium hosted jointly by Burpee Museum of Natural History and Northern Illinois University.][Henderson (2005). "Nano No More: The death of the pygmy tyrant." In "The origin, systematics, and paleobiology of Tyrannosauridae", a symposium hosted jointly by Burpee Museum of Natural History and Northern Illinois University.] Peter Larson continued to support the hypothesis that ''N''. ''lancensis'' was a separate but closely related species, based on skull features such as two more teeth in both jaws than ''T. rex''; as well as proportionately larger hands with phalanges on the third metacarpal and different wishbone
Wishbone commonly refers to:
* Furcula, a fork-shaped bone in birds and some dinosaurs
Wishbone may also refer to:
* Wish-Bone, an American salad dressing and condiment company
* Wishbone formation, a type of offense in American football
* Wish ...
anatomy in an undescribed specimen. He also argued that ''Stygivenator'', generally considered to be a juvenile ''T. rex'', may be a younger ''Nanotyrannus'' specimen.[Larson (2005). "A case for ''Nanotyrannus''." In "The origin, systematics, and paleobiology of Tyrannosauridae", a symposium hosted jointly by Burpee Museum of Natural History and Northern Illinois University.][Larson P (2013), "The validity of Nanotyrannus Lancensis (Theropoda, Lancian – Upper Maastrichtian of North America)", Society of Vertebrate Paleontology: 73rd annual meeting, ''Abstracts with Programs'', p. 159.] Later research revealed that other tyrannosaurids such as ''Gorgosaurus'' also experienced reduction in tooth count during growth,[ and given the disparity in tooth count between individuals of the same age group in this genus and ''Tyrannosaurus'', this feature may also be due to individual variation.] In 2013, Carr noted that all of the differences claimed to support ''Nanotyrannus'' have turned out to be individually or ontogenetically variable features or products of distortion of the bones.
In 2016, analysis of limb proportions by Persons and Currie suggested ''Nanotyrannus'' specimens to have differing cursoriality levels, potentially separating it from ''T. rex''. However, paleontologist Manabu Sakomoto has commented that this conclusion may be impacted by low sample size
Sample size determination is the act of choosing the number of observations or Replication (statistics), replicates to include in a statistical sample. The sample size is an important feature of any empirical study in which the goal is to make stat ...
, and the discrepancy does not necessarily reflect taxonomic distinction. In 2016, Joshua Schmerge argued for ''Nanotyrannus''' validity based on skull features, including a dentary groove in BMRP 2002.4.1's skull. According to Schmerge, as that feature is absent in ''T. rex'' and found only in ''Dryptosaurus'' and albertosaurines, this suggests ''Nanotyrannus'' is a distinct taxon within the Albertosaurinae. The same year, Carr and colleagues noted that this was not sufficient enough to clarify ''Nanotyrannus''' validity or classification, being a common and ontogenetically variable feature among tyrannosauroids.
A 2020 study by Holly Woodward and colleagues showed the specimens referred to ''Nanotyrannus'' were all ontogenetically immature and found it probable that these specimens belonged to ''T. rex''. The same year, Carr published a paper on ''T''. ''rex'''s growth history, finding that CMNH 7541 fit within the expected ontogenetic variation of the taxon and displayed juvenile characteristics found in other specimens. It was classified as a juvenile, under 13 years old with a skull less than . No significant sexual or phylogenetic variation was discernible among any of the 44 specimens studied, with Carr stating that characters of potential phylogenetic importance decrease throughout age at the same rate as growth occurs. Discussing the paper's results, Carr described how all "''Nanotyrannus''" specimens formed a continual growth transition between the smallest juveniles and the subadults, unlike what would be expected if it were a distinct taxon where the specimens would group to the exclusion of ''Tyrannosaurus''. Carr concluded that "the 'nanomorphs' are not all that similar to each other and instead form an important bridge in the growth series of ''T. rex'' that captures the beginnings of the profound change from the shallow skull of juveniles to the deep skull that is seen in fully-developed adults."
Paleobiology
Life history
The identification of several specimens as juvenile ''T. rex'' has allowed scientists to document ontogenetic
Ontogeny (also ontogenesis) is the origination and development of an organism (both physical and psychological, e.g., moral development), usually from the time of fertilization of the egg to adult. The term can also be used to refer to the st ...
changes in the species, estimate the lifespan, and determine how quickly the animals would have grown. The smallest known individual (LACM
The Natural History Museum of Los Angeles County is the largest natural and historical museum in the western United States. Its collections include nearly 35 million specimens and artifacts and cover 4.5 billion years of history. This large coll ...
28471, the "Jordan theropod") is estimated to have weighed only , while the largest, such as FMNH PR2081 (Sue) most likely weighed about . Histologic
Histology,
also known as microscopic anatomy or microanatomy, is the branch of biology which studies the microscopic anatomy of biological tissues. Histology is the microscopic counterpart to gross anatomy, which looks at larger structures vis ...
analysis of ''T. rex'' bones showed LACM 28471 had aged only 2 years when it died, while Sue was 28 years old, an age which may have been close to the maximum for the species.
Histology has also allowed the age of other specimens to be determined. Growth curves can be developed when the ages of different specimens are plotted on a graph along with their mass. A ''T. rex'' growth curve is S-shaped, with juveniles remaining under until approximately 14 years of age, when body size began to increase dramatically. During this rapid growth phase, a young ''T. rex'' would gain an average of a year for the next four years. At 18 years of age, the curve plateaus again, indicating that growth slowed dramatically. For example, only separated the 28-year-old Sue from a 22-year-old Canadian specimen ( RTMP 81.12.1). A 2004 histological study performed by different workers corroborates these results, finding that rapid growth began to slow at around 16 years of age.
A study by Hutchinson and colleagues in 2011 corroborated the previous estimation methods in general, but their estimation of peak growth rates is significantly higher; it found that the "maximum growth rates for T. rex during the exponential stage are 1790 kg/year". Although these results were much higher than previous estimations, the authors noted that these results significantly lowered the great difference between its actual growth rate and the one which would be expected of an animal of its size. The sudden change in growth rate at the end of the growth spurt may indicate physical maturity, a hypothesis which is supported by the discovery of medullary tissue in the femur
The femur (; ), or thigh bone, is the proximal bone of the hindlimb in tetrapod vertebrates. The head of the femur articulates with the acetabulum in the pelvic bone forming the hip joint, while the distal part of the femur articulates with ...
of a 16 to 20-year-old ''T. rex'' from Montana (MOR
Mor or MOR may refer to:
Names and titles
* Mór (given name), a list of people named Mór or Mor
* Mor (surname), a list of people named Mor or Mór
* Mor (honorific), or Mar, in Syriac
Radio and television
* Middle of the road (music) genre
* ...
1125, also known as B-rex). Medullary tissue is found only in female birds during ovulation, indicating that B-rex was of reproductive age. Further study indicates an age of 18 for this specimen. In 2016, it was finally confirmed by Mary Higby Schweitzer and Lindsay Zanno and colleagues that the soft tissue within the femur of MOR 1125 was medullary tissue. This also confirmed the identity of the specimen as a female. The discovery of medullary bone tissue within ''Tyrannosaurus'' may prove valuable in determining the sex of other dinosaur species in future examinations, as the chemical makeup of medullary tissue is unmistakable. Other tyrannosaurids exhibit extremely similar growth curves, although with lower growth rates corresponding to their lower adult sizes.
An additional study published in 2020 by Woodward and colleagues, for the journal ''Science Advances'' indicates that during their growth from juvenile to adult, ''Tyrannosaurus'' was capable of slowing down its growth to counter environmental factors such as lack of food. The study, focusing on two juvenile specimens between 13 and 15 years old housed at the Burpee Museum in Illinois, indicates that the rate of maturation for ''Tyrannosaurus'' was dependent on resource abundance. This study also indicates that in such changing environments, ''Tyrannosaurus'' was particularly well-suited to an environment that shifted yearly in regards to resource abundance, hinting that other midsize predators might have had difficulty surviving in such harsh conditions and explaining the niche partitioning between juvenile and adult tyrannosaurs. The study further indicates that ''Tyrannosaurus'' and the dubious genus ''Nanotyrannus'' are synonymous, due to analysis of the growth rings in the bones of the two specimens studied.
Over half of the known ''T. rex'' specimens appear to have died within six years of reaching sexual maturity, a pattern which is also seen in other tyrannosaurs and in some large, long-lived birds and mammals today. These species are characterized by high infant mortality rates, followed by relatively low mortality among juveniles. Mortality increases again following sexual maturity, partly due to the stresses of reproduction. One study suggests that the rarity of juvenile ''T. rex'' fossils is due in part to low juvenile mortality rates; the animals were not dying in large numbers at these ages, and thus were not often fossilized. This rarity may also be due to the incompleteness of the fossil record or to the bias of fossil collectors towards larger, more spectacular specimens. In a 2013 lecture, Thomas Holtz Jr. suggested that dinosaurs "lived fast and died young" because they reproduced quickly whereas mammals have long life spans because they take longer to reproduce. Gregory S. Paul also writes that ''Tyrannosaurus'' reproduced quickly and died young, but attributes their short life spans to the dangerous lives they lived.
Skin and possible filamentous feathering
The discovery of feathered dinosaur
A feathered dinosaur is any species of dinosaur possessing feathers. While this includes all species of birds, there is a hypothesis that many, if not all non-avian dinosaur species also possessed feathers in some shape or form.
It has been su ...
s led to debate regarding whether, and to what extent, ''Tyrannosaurus'' might have been feathered. Filamentous structures, which are commonly recognized as the precursors of feather
Feathers are epidermal growths that form a distinctive outer covering, or plumage, on both avian (bird) and some non-avian dinosaurs and other archosaurs. They are the most complex integumentary structures found in vertebrates and a premier ...
s, have been reported in the small-bodied, basal tyrannosauroid '' Dilong paradoxus'' from the Early Cretaceous Yixian Formation of China in 2004. Because integumentary impressions of larger tyrannosauroids known at that time showed evidence of scales
Scale or scales may refer to:
Mathematics
* Scale (descriptive set theory), an object defined on a set of points
* Scale (ratio), the ratio of a linear dimension of a model to the corresponding dimension of the original
* Scale factor, a number w ...
, the researchers who studied ''Dilong'' speculated that insulating feathers might have been lost by larger species due to their smaller surface-to-volume ratio. The subsequent discovery of the giant species ''Yutyrannus huali
''Yutyrannus'' (meaning "feathered tyrant") is a genus of proceratosaurid tyrannosauroid dinosaur which contains a single known species, ''Yutyrannus huali''. This species lived during the early Cretaceous period in what is now northeastern Chi ...
'', also from the Yixian, showed that even some large tyrannosauroids had feathers covering much of their bodies, casting doubt on the hypothesis that they were a size-related feature. A 2017 study reviewed known skin impressions of tyrannosaurids, including those of a ''Tyrannosaurus'' specimen nicknamed "Wyrex" (BHI 6230) which preserves patches of mosaic scales on the tail, hip, and neck. The study concluded that feather covering of large tyrannosaurids such as ''Tyrannosaurus'' was, if present, limited to the upper side of the trunk.
A conference abstract published in 2016 posited that theropods such as ''Tyrannosaurus'' had their upper teeth covered in lips, instead of bare teeth as seen in crocodilia
Crocodilia (or Crocodylia, both ) is an order of mostly large, predatory, semiaquatic reptiles, known as crocodilians. They first appeared 95 million years ago in the Late Cretaceous period ( Cenomanian stage) and are the closest living ...
ns. This was based on the presence of enamel, which according to the study needs to remain hydrated, an issue not faced by aquatic animals like crocodilians. A 2017 analytical study proposed that tyrannosaurids had large, flat scales on their snouts instead of lips. However, there has been criticism where it favors the idea for lips. Crocodiles do not really have flat scales but rather cracked keratinized skin; by observing the hummocky rugosity of tyrannosaurids, and comparing it to extant lizards they found that tyrannosaurids had squamose scales rather than a crocodillian-like skin.
Sexual dimorphism
As the number of known specimens increased, scientists began to analyze the variation between individuals and discovered what appeared to be two distinct body types, or ''morphs'', similar to some other theropod species. As one of these morphs was more solidly built, it was termed the 'robust' morph while the other was termed 'gracile
Gracility is slenderness, the condition of being gracile, which means slender. It derives from the Latin adjective ''gracilis'' (masculine or feminine), or ''gracile'' ( neuter), which in either form means slender, and when transferred for examp ...
'. Several morphological differences associated with the two morphs were used to analyze sexual dimorphism
Sexual dimorphism is the condition where the sexes of the same animal and/or plant species exhibit different morphological characteristics, particularly characteristics not directly involved in reproduction. The condition occurs in most ani ...
in ''T. rex'', with the 'robust' morph usually suggested to be female. For example, the pelvis
The pelvis (plural pelves or pelvises) is the lower part of the trunk, between the abdomen and the thighs (sometimes also called pelvic region), together with its embedded skeleton (sometimes also called bony pelvis, or pelvic skeleton).
The ...
of several 'robust' specimens seemed to be wider, perhaps to allow the passage of eggs. It was also thought that the 'robust' morphology correlated with a reduced chevron
Chevron (often relating to V-shaped patterns) may refer to:
Science and technology
* Chevron (aerospace), sawtooth patterns on some jet engines
* Chevron (anatomy), a bone
* ''Eulithis testata'', a moth
* Chevron (geology), a fold in rock lay ...
on the first tail vertebra, also ostensibly to allow eggs to pass out of the reproductive tract
The reproductive system of an organism, also known as the genital system, is the biological system made up of all the anatomical sex organs, organs involved in sexual reproduction. Many non-living substances such as fluids, hormones, and pherom ...
, as had been erroneously reported for crocodile
Crocodiles (family (biology), family Crocodylidae) or true crocodiles are large semiaquatic reptiles that live throughout the tropics in Africa, Asia, the Americas and Australia. The term crocodile is sometimes used even more loosely to inclu ...
s.
In recent years, evidence for sexual dimorphism has been weakened. A 2005 study reported that previous claims of sexual dimorphism in crocodile chevron anatomy were in error, casting doubt on the existence of similar dimorphism between ''T. rex'' sexes. A full-sized chevron was discovered on the first tail vertebra of Sue, an extremely robust individual, indicating that this feature could not be used to differentiate the two morphs anyway. As ''T. rex'' specimens have been found from Saskatchewan
Saskatchewan ( ; ) is a Provinces and territories of Canada, province in Western Canada, western Canada, bordered on the west by Alberta, on the north by the Northwest Territories, on the east by Manitoba, to the northeast by Nunavut, and on t ...
to New Mexico
)
, population_demonym = New Mexican ( es, Neomexicano, Neomejicano, Nuevo Mexicano)
, seat = Santa Fe
, LargestCity = Albuquerque
, LargestMetro = Tiguex
, OfficialLang = None
, Languages = English, Spanish ( New Mexican), Navajo, Ker ...
, differences between individuals may be indicative of geographic variation rather than sexual dimorphism. The differences could also be age-related, with 'robust' individuals being older animals.
Only a single ''Tyrannosaurus'' specimen has been conclusively shown to belong to a specific sex. Examination of B-rex demonstrated the preservation of soft tissue within several bones. Some of this tissue has been identified as a medullary tissue, a specialized tissue grown only in modern birds as a source of calcium
Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar to ...
for the production of eggshell
An eggshell is the outer covering of a hard-shelled egg and of some forms of eggs with soft outer coats.
Diversity
Worm eggs
Nematode eggs present a two layered structure: an external vitellin layer made of chitin that confers mechanical ...
during ovulation. As only female birds lay eggs, medullary tissue is only found naturally in females, although males are capable of producing it when injected with female reproductive hormone
A hormone (from the Greek participle , "setting in motion") is a class of signaling molecules in multicellular organisms that are sent to distant organs by complex biological processes to regulate physiology and behavior. Hormones are required ...
s like estrogen
Estrogen or oestrogen is a category of sex hormone responsible for the development and regulation of the female reproductive system and secondary sex characteristics. There are three major endogenous estrogens that have estrogenic hormonal acti ...
. This strongly suggests that B-rex was female and that she died during ovulation. Recent research has shown that medullary tissue is never found in crocodiles, which are thought to be the closest living relatives of dinosaurs, aside from birds. The shared presence of medullary tissue in birds and theropod dinosaurs is further evidence of the close evolution
Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation ...
ary relationship between the two.
Posture
Like many bipedal dinosaurs, ''T. rex'' was historically depicted as a 'living tripod', with the body at 45 degrees or less from the vertical and the tail dragging along the ground, similar to a kangaroo
Kangaroos are four marsupials from the family Macropodidae (macropods, meaning "large foot"). In common use the term is used to describe the largest species from this family, the red kangaroo, as well as the antilopine kangaroo, eastern gre ...
. This concept dates from Joseph Leidy's 1865 reconstruction of '' Hadrosaurus'', the first to depict a dinosaur in a bipedal posture. In 1915, convinced that the creature stood upright, Henry Fairfield Osborn, former president of the American Museum of Natural History, further reinforced the notion in unveiling the first complete ''T. rex'' skeleton arranged this way. It stood in an upright pose for 77 years, until it was dismantled in 1992.
By 1970, scientists realized this pose was incorrect and could not have been maintained by a living animal, as it would have resulted in the dislocation
In materials science, a dislocation or Taylor's dislocation is a linear crystallographic defect or irregularity within a crystal structure that contains an abrupt change in the arrangement of atoms. The movement of dislocations allow atoms to sl ...
or weakening of several joints, including the hips and the articulation between the head and the spinal column
The vertebral column, also known as the backbone or spine, is part of the axial skeleton. The vertebral column is the defining characteristic of a vertebrate in which the notochord (a flexible rod of uniform composition) found in all chordates ...
. The inaccurate AMNH mount inspired similar depictions in many films and paintings (such as Rudolph Zallinger
Rudolph Franz Zallinger (; November 12, 1919 – August 1, 1995) was an American-based Austrian-Russian artist. His most notable works include his mural '' The Age of Reptiles'' (1947) at Yale University's Peabody Museum of Natural History, and t ...
's famous mural ''The Age of Reptiles
''The Age of Reptiles'' is a mural depicting the period of ancient history when reptiles were the dominant creatures on the earth, painted by Rudolph Zallinger. The fresco sits in the Yale Peabody Museum in New Haven, Connecticut, and was comp ...
'' in Yale University
Yale University is a private research university in New Haven, Connecticut. Established in 1701 as the Collegiate School, it is the third-oldest institution of higher education in the United States and among the most prestigious in the wo ...
's Peabody Museum of Natural History) until the 1990s, when films such as ''Jurassic Park
''Jurassic Park'', later also referred to as ''Jurassic World'', is an American science fiction media franchise created by Michael Crichton and centered on a disastrous attempt to create a theme park of cloned dinosaurs. It began in 1990 when ...
'' introduced a more accurate posture to the general public. Modern representations in museums, art, and film show ''T. rex'' with its body approximately parallel to the ground with the tail extended behind the body to balance the head.
To sit down, ''Tyrannosaurus'' may have settled its weight backwards and rested its weight on a pubic boot, the wide expansion at the end of the pubis in some dinosaurs. With its weight rested on the pelvis, it may have been free to move the hindlimbs. Getting back up again might have involved some stabilization from the diminutive forelimbs. The latter known as Newman's pushup theory has been debated. Nonetheless, ''Tyrannosaurus'' was probably able to get up if it fell, which only would have required placing the limbs below the center of gravity, with the tail as an effective counterbalance. Healed stress fractures in the forelimbs have been put forward both as evidence that the arms cannot have been very useful and as evidence that they were indeed used and acquired wounds,[Stevens K.A., Larson P, Willis E.D. & Anderson A. "Rex, sit: digital modeling of ''Tyrannosaurus rex'' at rest". In Larson P & Carpenter K (eds.). ''Tyrannosaurus rex, the tyrant king'' (Indiana University Press, 2008). p. 192-203] like the rest of the body.
Arms
When ''T. rex'' was first discovered, the humerus
The humerus (; ) is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius and ulna, and consists of three sections. The humeral upper extremity consists of a roun ...
was the only element of the forelimb known.[ Retrieved October 6, 2008.] For the initial mounted skeleton as seen by the public in 1915, Osborn substituted longer, three-fingered forelimbs like those of '' Allosaurus''. A year earlier, Lawrence Lambe
Lawrence Morris Lambe (August 27, 1863 – March 12, 1919) was a Canadian geologist, palaeontologist, and ecologist from the Geological Survey of Canada (GSC).
His published work, describing the diverse and plentiful dinosaur discoveries from th ...
described the short, two-fingered forelimbs of the closely related ''Gorgosaurus''. This strongly suggested that ''T. rex'' had similar forelimbs, but this hypothesis
A hypothesis (plural hypotheses) is a proposed explanation for a phenomenon. For a hypothesis to be a scientific hypothesis, the scientific method requires that one can test it. Scientists generally base scientific hypotheses on previous obse ...
was not confirmed until the first complete ''T. rex'' forelimbs were identified in 1989, belonging to MOR 555 (the "Wankel rex"). The remains of Sue also include complete forelimbs. ''T. rex'' arms are very small relative to overall body size, measuring only long, and some scholars have labelled them as vestigial
Vestigiality is the retention, during the process of evolution, of genetically determined structures or attributes that have lost some or all of the ancestral function in a given species. Assessment of the vestigiality must generally rely on co ...
. However, the bones show large areas for muscle
Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of muscl ...
attachment, indicating considerable strength. This was recognized as early as 1906 by Osborn, who speculated that the forelimbs may have been used to grasp a mate during copulation
Sexual intercourse (or coitus or copulation) is a sexual activity typically involving the insertion and thrusting of the penis into the vagina for sexual pleasure or reproduction.Sexual intercourse most commonly means penile–vaginal penetrat ...
. Newman (1970) suggested that the forelimbs were used to assist ''Tyrannosaurus'' in rising from a prone position. Since then, other functions have been proposed, although some scholars find them implausible. Padian (2022) argued that the reduction of the arms in tyrannosaurids did not serve a particular function but was a secondary adaptation; stating that as tyrannosaurids developed larger and more powerful skulls and jaws, the arms got smaller to avoid being bitten or torn by other individuals, particularly during group feedings.[Padian K (2022)]
"Why tyrannosaurid forelimbs were so short: An integrative hypothesis"
''Acta Palaeontologica Polonica'' 67(1): p. 63-76
Another possibility is that the forelimbs held struggling prey while it was killed by the tyrannosaur's enormous jaws. This hypothesis may be supported by biomechanical analysis. ''T. rex'' forelimb bones exhibit extremely thick cortical bone, which has been interpreted as evidence that they were developed to withstand heavy loads. The biceps brachii
The biceps or biceps brachii ( la, musculus biceps brachii, "two-headed muscle of the arm") is a large muscle that lies on the front of the upper arm between the shoulder and the elbow. Both heads of the muscle arise on the scapula and join t ...
muscle of an adult ''T. rex'' was capable of lifting by itself; other muscles such as the brachialis
The brachialis (brachialis anticus), also known as the Teichmann muscle, is a muscle in the upper arm that flexes the elbow. It lies deeper than the biceps brachii, and makes up part of the floor of the region known as the cubital fossa (elbow pi ...
would work along with the biceps to make elbow flexion even more powerful. The M. biceps
The biceps or biceps brachii ( la, musculus biceps brachii, "two-headed muscle of the arm") is a large muscle that lies on the front of the upper arm between the shoulder and the elbow. Both heads of the muscle arise on the scapula and join ...
muscle of ''T. rex'' was 3.5 times as powerful as the human equivalent The term human equivalent is used in a number of different contexts. This term can refer to human equivalents of various comparisons of animate and inanimate things.
Animal models in chemistry and medicine
Animal models are used to learn more abou ...
. A ''T. rex'' forearm had a limited range of motion, with the shoulder and elbow joints allowing only 40 and 45 degrees of motion, respectively. In contrast, the same two joints in '' Deinonychus'' allow up to 88 and 130 degrees of motion, respectively, while a human arm can rotate 360 degrees at the shoulder and move through 165 degrees at the elbow. The heavy build of the arm bones, strength of the muscles, and limited range of motion may indicate a system evolved to hold fast despite the stresses of a struggling prey animal. In the first detailed scientific description of ''Tyrannosaurus'' forelimbs, paleontologists Kenneth Carpenter and Matt Smith dismissed notions that the forelimbs were useless or that ''Tyrannosaurus'' was an obligate scavenger.
The idea that the arms served as weapons when hunting prey have also been proposed by Steven M. Stanley
Steven M. Stanley (born November 2, 1941) is an American paleontologist and evolutionary biologist at the University of Hawaii at Manoa. He is best known for his empirical research documenting the evolutionary process of punctuated equilibrium in t ...
, who suggested that the arms were used for slashing prey, especially by using the claws to rapidly inflict long, deep gashes to its prey. This was dismissed by Padian, who have argued that Stanley based his conclusion on incorrectly estimated forelimb size and range of motion.
Thermoregulation
''Tyrannosaurus'', like most dinosaurs, was long thought to have an ectotherm
An ectotherm (from the Greek () "outside" and () "heat") is an organism in which internal physiological sources of heat are of relatively small or of quite negligible importance in controlling body temperature.Davenport, John. Animal Life a ...
ic ("cold-blooded") reptilian metabolism
Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cell ...
. The idea of dinosaur ectothermy was challenged by scientists like Robert T. Bakker
Robert Thomas Bakker (born March 24, 1945) is an American paleontologist who helped reshape modern theories about dinosaurs, particularly by adding support to the theory that some dinosaurs were endothermic (warm-blooded). Along with his mentor J ...
and John Ostrom in the early years of the " Dinosaur Renaissance", beginning in the late 1960s. ''T. rex'' itself was claimed to have been endothermic
In thermochemistry, an endothermic process () is any thermodynamic process with an increase in the enthalpy (or internal energy ) of the system.Oxtoby, D. W; Gillis, H.P., Butler, L. J. (2015).''Principle of Modern Chemistry'', Brooks Cole. p. ...
("warm-blooded"), implying a very active lifestyle. Since then, several paleontologists have sought to determine the ability of ''Tyrannosaurus'' to regulate
Regulate may refer to:
* Regulation
* '' Regulate...G Funk Era'', an album from rapper Warren G
** Regulate (song), title song from the album
See also
*
*
* Regulator (disambiguation)
Regulator may refer to:
Technology
* Regulator (automati ...
its body temperature. Histological evidence of high growth rates in young ''T. rex'', comparable to those of mammals and birds, may support the hypothesis of a high metabolism. Growth curves indicate that, as in mammals and birds, ''T. rex'' growth was limited mostly to immature animals, rather than the indeterminate growth seen in most other vertebrate
Vertebrates () comprise all animal taxa within the subphylum Vertebrata () ( chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, ...
s.
Oxygen isotope
There are three known stable isotopes of oxygen (8O): , , and .
Radioactive isotopes ranging from to have also been characterized, all short-lived. The longest-lived radioisotope is with a half-life of , while the shortest-lived isotope is ...
ratios in fossilized bone are sometimes used to determine the temperature at which the bone was deposited, as the ratio between certain isotopes correlates with temperature. In one specimen, the isotope ratios in bones from different parts of the body indicated a temperature difference of no more than 4 to 5 °C (7 to 9 °F) between the vertebrae of the torso and the tibia
The tibia (; ), also known as the shinbone or shankbone, is the larger, stronger, and anterior (frontal) of the two bones in the leg below the knee in vertebrates (the other being the fibula, behind and to the outside of the tibia); it connects ...
of the lower leg. This small temperature range between the body core and the extremities was claimed by paleontologist Reese Barrick and geochemist
Geochemistry is the science that uses the tools and principles of chemistry to explain the mechanisms behind major geological systems such as the Earth's crust and its oceans. The realm of geochemistry extends beyond the Earth, encompassing the ...
William Showers to indicate that ''T. rex'' maintained a constant internal body temperature ( homeothermy) and that it enjoyed a metabolism somewhere between ectothermic reptiles and endothermic mammals. Other scientists have pointed out that the ratio of oxygen isotopes in the fossils today does not necessarily represent the same ratio in the distant past, and may have been altered during or after fossilization ( diagenesis). Barrick and Showers have defended their conclusions in subsequent papers, finding similar results in another theropod dinosaur from a different continent and tens of millions of years earlier in time ('' Giganotosaurus''). Ornithischia
Ornithischia () is an extinct order of mainly herbivorous dinosaurs characterized by a pelvic structure superficially similar to that of birds. The name ''Ornithischia'', or "bird-hipped", reflects this similarity and is derived from the Greek s ...
n dinosaurs also showed evidence of homeothermy, while varanid
The Varanidae are a family of lizards in the superfamily Varanoidea within the Anguimorpha group. The family, a group of carnivorous and frugivorous lizards, includes the living genus '' Varanus'' and a number of extinct genera more closely relat ...
lizard
Lizards are a widespread group of squamate reptiles, with over 7,000 species, ranging across all continents except Antarctica, as well as most oceanic island chains. The group is paraphyletic since it excludes the snakes and Amphisbaenia alt ...
s from the same formation did not. In 2022, Wiemann and colleagues used a different approach—the spectroscopy
Spectroscopy is the field of study that measures and interprets the electromagnetic spectra that result from the interaction between electromagnetic radiation and matter as a function of the wavelength or frequency of the radiation. Matter wa ...
of lipoxidation signals, which are byproducts of oxidative phosphorylation
Oxidative phosphorylation (UK , US ) or electron transport-linked phosphorylation or terminal oxidation is the metabolic pathway in which cells use enzymes to oxidize nutrients, thereby releasing chemical energy in order to produce adenosine tri ...
and correlate with metabolic rates—to show that various dinosaur genera including ''Tyrannosaurus'' had endothermic metabolisms, on par with that of modern birds and higher than that of mammals. They also suggested that such a metabolism was ancestrally common to all dinosaurs.
Even if ''T. rex'' does exhibit evidence of homeothermy, it does not necessarily mean that it was endothermic. Such thermoregulation may also be explained by gigantothermy, as in some living sea turtle
Sea turtles (superfamily Chelonioidea), sometimes called marine turtles, are reptiles of the order Testudines and of the suborder Cryptodira. The seven existing species of sea turtles are the flatback, green, hawksbill, leatherback, loggerhead, ...
s. Similar to contemporary crocodilians, openings (dorsotemporal fenestrae) in the skull roofs of ''Tyrannosaurus'' may have aided thermoregulation.
Soft tissue
In the March 2005 issue of ''Science
Science is a systematic endeavor that builds and organizes knowledge in the form of testable explanations and predictions about the universe.
Science may be as old as the human species, and some of the earliest archeological evidence for ...
'', Mary Higby Schweitzer
Mary Higby Schweitzer is an American paleontologist at North Carolina State University, who led the groups that discovered the remains of blood cells in dinosaur fossils and later discovered soft tissue remains in the ''Tyrannosaurus rex'' specime ...
of North Carolina State University
North Carolina State University (NC State) is a public land-grant research university in Raleigh, North Carolina. Founded in 1887 and part of the University of North Carolina system, it is the largest university in the Carolinas. The universit ...
and colleagues announced the recovery of soft tissue from the marrow cavity of a fossilized leg bone from a ''T. rex''. The bone had been intentionally, though reluctantly, broken for shipping and then not preserved in the normal manner, specifically because Schweitzer was hoping to test it for soft tissue. Designated as the Museum of the Rockies specimen 1125, or MOR 1125, the dinosaur was previously excavated from the Hell Creek Formation. Flexible, bifurcating blood vessel
The blood vessels are the components of the circulatory system that transport blood throughout the human body. These vessels transport blood cells, nutrients, and oxygen to the tissues of the body. They also take waste and carbon dioxide away ...
s and fibrous but elastic bone
A bone is a Stiffness, rigid Organ (biology), organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red blood cell, red and white blood cells, store minerals, provid ...
matrix tissue were recognized. In addition, microstructures resembling blood cell
A blood cell, also called a hematopoietic cell, hemocyte, or hematocyte, is a cell produced through hematopoiesis and found mainly in the blood. Major types of blood cells include red blood cells (erythrocytes), white blood cells (leukocytes), ...
s were found inside the matrix and vessels. The structures bear resemblance to ostrich
Ostriches are large flightless birds of the genus ''Struthio'' in the order Struthioniformes, part of the infra-class Palaeognathae, a diverse group of flightless birds also known as ratites that includes the emus, rheas, and kiwis. There are ...
blood cells and vessels. Whether an unknown process, distinct from normal fossilization, preserved the material, or the material is original, the researchers do not know, and they are careful not to make any claims about preservation. If it is found to be original material, any surviving proteins may be used as a means of indirectly guessing some of the DNA content of the dinosaurs involved, because each protein is typically created by a specific gene. The absence of previous finds may be the result of people assuming preserved tissue was impossible, therefore not looking. Since the first, two more tyrannosaurs and a hadrosaur have also been found to have such tissue-like structures. Research on some of the tissues involved has suggested that birds are closer relatives to tyrannosaurs than other modern animals.
In studies reported in ''Science'' in April 2007, Asara and colleagues concluded that seven traces of collagen
Collagen () is the main structural protein in the extracellular matrix found in the body's various connective tissues. As the main component of connective tissue, it is the most abundant protein in mammals, making up from 25% to 35% of the whole ...
proteins detected in purified ''T. rex'' bone most closely match those reported in chicken
The chicken (''Gallus gallus domesticus'') is a domesticated junglefowl species, with attributes of wild species such as the grey and the Ceylon junglefowl that are originally from Southeastern Asia. Rooster or cock is a term for an adult m ...
s, followed by frogs and newts. The discovery of proteins from a creature tens of millions of years old, along with similar traces the team found in a mastodon bone at least 160,000 years old, upends the conventional view of fossils and may shift paleontologists' focus from bone hunting to biochemistry. Until these finds, most scientists presumed that fossilization replaced all living tissue with inert minerals. Paleontologist Hans Larsson of McGill University in Montreal, who was not part of the studies, called the finds "a milestone", and suggested that dinosaurs could "enter the field of molecular biology and really slingshot paleontology into the modern world".
The presumed soft tissue was called into question by Thomas Kaye of the University of Washington
The University of Washington (UW, simply Washington, or informally U-Dub) is a public research university in Seattle, Washington.
Founded in 1861, Washington is one of the oldest universities on the West Coast; it was established in Seattle a ...
and his co-authors in 2008. They contend that what was really inside the tyrannosaur bone was slimy biofilm
A biofilm comprises any syntrophic consortium of microorganisms in which cells stick to each other and often also to a surface. These adherent cells become embedded within a slimy extracellular matrix that is composed of extracellular ...
created by bacteria that coated the voids once occupied by blood vessels and cells. The researchers found that what previously had been identified as remnants of blood cells, because of the presence of iron, were actually framboid A framboid is a micromorphological feature common to certain sedimentary minerals, particularly pyrite (FeS2). The first known use of the term is ascribed to Rust in 1935 and is derived from the French ‘la framboise’, meaning ‘raspberry’, re ...
s, microscopic mineral spheres bearing iron. They found similar spheres in a variety of other fossils from various periods, including an ammonite
Ammonoids are a group of extinct marine mollusc animals in the subclass Ammonoidea of the class Cephalopoda. These molluscs, commonly referred to as ammonites, are more closely related to living coleoids (i.e., octopuses, squid and cuttlefish) ...
. In the ammonite, they found the spheres in a place where the iron they contain could not have had any relationship to the presence of blood. Schweitzer has strongly criticized Kaye's claims and argues that there is no reported evidence that biofilms can produce branching, hollow tubes like those noted in her study. San Antonio, Schweitzer and colleagues published an analysis in 2011 of what parts of the collagen had been recovered, finding that it was the inner parts of the collagen coil that had been preserved, as would have been expected from a long period of protein degradation. Other research challenges the identification of soft tissue as biofilm and confirms finding "branching, vessel-like structures" from within fossilized bone.
Speed
Scientists have produced a wide range of possible maximum running speeds for ''Tyrannosaurus'': mostly around , but as low as and as high as , though it running this speed is very unlikely. ''Tyrannosaurus'' was a bulky and heavy carnivore so it is unlikely to run very fast at all compared to other theropods like '' Carnotaurus'' or '' Giganotosaurus''. Researchers have relied on various estimating techniques because, while there are many tracks of large theropods walking, none showed evidence of running.
A 2002 report used a mathematical model (validated by applying it to three living animals: alligator
An alligator is a large reptile in the Crocodilia order in the genus ''Alligator'' of the family Alligatoridae. The two extant species are the American alligator (''A. mississippiensis'') and the Chinese alligator (''A. sinensis''). Additiona ...
s, chicken
The chicken (''Gallus gallus domesticus'') is a domesticated junglefowl species, with attributes of wild species such as the grey and the Ceylon junglefowl that are originally from Southeastern Asia. Rooster or cock is a term for an adult m ...
s, and human
Humans (''Homo sapiens'') are the most abundant and widespread species of primate, characterized by bipedalism and exceptional cognitive skills due to a large and complex brain. This has enabled the development of advanced tools, culture, ...
s; and eight more species, including emus and ostriches) to gauge the leg muscle mass needed for fast running (over ). Scientists who think that ''Tyrannosaurus'' was able to run point out that hollow bones and other features that would have lightened its body may have kept adult weight to a mere or so, or that other animals like ostrich
Ostriches are large flightless birds of the genus ''Struthio'' in the order Struthioniformes, part of the infra-class Palaeognathae, a diverse group of flightless birds also known as ratites that includes the emus, rheas, and kiwis. There are ...
es and horse
The horse (''Equus ferus caballus'') is a domesticated, one-toed, hoofed mammal. It belongs to the taxonomic family Equidae and is one of two extant subspecies of ''Equus ferus''. The horse has evolved over the past 45 to 55 million y ...
s with long, flexible legs are able to achieve high speeds through slower but longer strides. Proposed top speeds exceeded for ''Tyrannosaurus'', but were deemed infeasible because they would require exceptional leg muscles of approximately 40–86% of total body mass. Even moderately fast speeds would have required large leg muscles. If the muscle mass was less, only for walking or jogging would have been possible. Holtz noted that tyrannosaurids and some closely related groups had significantly longer distal
Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position pro ...
hindlimb components (shin plus foot plus toes) relative to the femur length than most other theropods, and that tyrannosaurids and their close relatives had a tightly interlocked metatarsus (foot bones). The third metatarsal was squeezed between the second and fourth metatarsals to form a single unit called an arctometatarsus
An arctometatarsalian organism is one in which the proximal part of the middle metatarsal is pinched between the surrounding metatarsals. The trait appears to be highly homoplastic, common in certain sorts of dinosaurs accustomed to running (among ...
. This ankle feature may have helped the animal to run more efficiently. Together, these leg features allowed ''Tyrannosaurus'' to transmit locomotory forces from the foot to the lower leg more effectively than in earlier theropods.
Additionally, a 2020 study indicates that ''Tyrannosaurus'' and other tyrannosaurids were exceptionally efficient walkers. Studies by Dececchi ''et al.'', compared the leg proportions, body mass, and the gaits of more than 70 species of theropod dinosaurs including ''Tyrannosaurus'' and its relatives. The research team then applied a variety of methods to estimate each dinosaur's top speed when running as well as how much energy each dinosaur expended while moving at more relaxed speeds such as when walking. Among smaller to medium-sized species such as dromaeosaurids, longer legs appear to be an adaptation for faster running, in line with previous results by other researchers. But for theropods weighing over , top running speed is limited by body size, so longer legs instead were found to have correlated with low-energy walking. The results further indicate that smaller theropods evolved long legs as a means to both aid in hunting and escape from larger predators while larger theropods that evolved long legs did so to reduce the energy costs and increase foraging efficiency, as they were freed from the demands of predation pressure due to their role as apex predators. Compared to more basal groups of theropods in the study, tyrannosaurs like ''Tyrannosaurus'' itself showed a marked increase in foraging efficiency due to reduced energy expenditures during hunting or scavenging. This in turn likely resulted in tyrannosaurs having a reduced need for hunting forays and requiring less food to sustain themselves as a result. Additionally, the research, in conjunction with studies that show tyrannosaurs were more agile than other large-bodied theropods, indicates they were quite well-adapted to a long-distance stalking approach followed by a quick burst of speed to go for the kill. Analogies can be noted between tyrannosaurids and modern wolves as a result, supported by evidence that at least some tyrannosaurids were hunting in group settings.
A study published in 2021 by Pasha van Bijlert ''et al.'', calculated the preferred walking speed of ''Tyrannosaurus'', reporting a speed of . While walking, animals reduce their energy expenditure In biology, energy homeostasis, or the homeostatic control of energy balance, is a biological process that involves the coordinated homeostatic regulation of food intake (energy inflow) and energy expenditure (energy outflow). The human brain, parti ...
by choosing certain step rhythms at which their body parts resonate. The same would have been true for dinosaurs
Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...
, but previous studies did not fully account for the impact the tail had on their walking speeds. According to the authors, when a dinosaur walked, its tail would slightly sway up and down with each step as a result of the interspinous ligaments
The interspinous ligaments (interspinal ligaments) are thin and membranous ligaments, that connect adjoining spinous processes of the vertebra in the spine.
They extend from the root to the apex of each spinous process. They meet the ligamenta fl ...
suspending the tail. Like rubber bands, these ligaments stored energy when they are stretched due to the swaying of the tail. Using a 3-D model of ''Tyrannosaurus'' specimen Trix, muscles and ligaments were reconstructed to simulate the tail movements. This results in a rhythmic, energy-efficient walking speed for ''Tyrannosaurus'' similar to that seen in living animals such as humans, ostriches and giraffes.
A 2017 study estimated the top running speed of ''Tyrannosaurus'' as 17 mph (27 km/h), speculating that ''Tyrannosaurus'' exhausted its energy reserves long before reaching top speed, resulting in a parabola-like relationship between size and speed. Another 2017 study hypothesized that an adult ''Tyrannosaurus'' was incapable of running due to high skeletal loads. Using a calculated weight estimate of 7 tons, the model showed that speeds above 11 mph (18 km/h) would have probably shattered the leg bones of ''Tyrannosaurus''. The finding may mean that running was also not possible for other giant theropod dinosaurs like '' Giganotosaurus'', '' Mapusaurus'' and '' Acrocanthosaurus''.
However, studies by Eric Snively and colleagues'','' published in 2019 indicate that ''Tyrannosaurus'' and other tyrannosaurids were more maneuverable than allosauroids and other theropods of comparable size due to low rotational inertia compared to their body mass combined with large leg muscles. As a result, it is hypothesized that ''Tyrannosaurus'' was capable of making relatively quick turns and could likely pivot its body more quickly when close to its prey, or that while turning, the theropod could "pirouette" on a single planted foot while the alternating leg was held out in a suspended swing during a pursuit. The results of this study potentially could shed light on how agility could have contributed to the success of tyrannosaurid evolution.
Possible footprints
Rare fossil footprints and trackways found in New Mexico and Wyoming that are assigned to the ichnogenus '' Tyrannosauripus'' have been attributed to being made by ''Tyrannosaurus'', based on the stratigraphic age of the rocks they are preserved in. The first specimen, found in 1994 was described by Lockley and Hunt and consists of a single, large footprint. Another pair of ichnofossils, described in 2021, show a large tyrannosaurid rising from a prone position by rising up using its elbows in conjunction with the pads on their feet to stand. These two unique sets of fossils were found in Ludlow, Colorado and Cimarron, New Mexico. Another ichnofossil described in 2018, perhaps belonging to a juvenile ''Tyrannosaurus'' or the dubious genus ''Nanotyrannus'' was uncovered in the Lance Formation of Wyoming. The trackway itself offers a rare glimpse into the walking speed of tyrannosaurids, and the trackmaker is estimated to have been moving at a speed of , significantly faster than previously assumed for estimations of walking speed in tyrannosaurids.
Brain and senses
A study conducted by Lawrence Witmer
Lawrence M. Witmer (born October 10, 1959, at Rochester, New York) is an American paleontologist and paleobiologist. He is a Professor of Anatomy and a Chang Ying-Chien Professor of Paleontology at the Department of Biomedical Sciences at the Her ...
and Ryan Ridgely of Ohio University found that ''Tyrannosaurus'' shared the heightened sensory abilities of other coelurosaur
Coelurosauria (; from Greek, meaning "hollow tailed lizards") is the clade containing all theropod dinosaurs more closely related to birds than to carnosaurs.
Coelurosauria is a subgroup of theropod dinosaurs that includes compsognathids, tyrann ...
s, highlighting relatively rapid and coordinated eye and head movements; an enhanced ability to sense low frequency sounds, which would allow tyrannosaurs to track prey movements from long distances; and an enhanced sense of smell. A study published by Kent Stevens concluded that ''Tyrannosaurus'' had keen vision. By applying modified perimetry to facial reconstructions of several dinosaurs including ''Tyrannosaurus'', the study found that ''Tyrannosaurus'' had a binocular range of 55 degrees, surpassing that of modern hawks. Stevens estimated that ''Tyrannosaurus'' had 13 times the visual acuity of a human and surpassed the visual acuity of an eagle, which is 3.6 times that of a person. Stevens estimated a limiting far point (that is, the distance at which an object can be seen as separate from the horizon) as far as away, which is greater than the that a human can see.
Thomas Holtz Jr. would note that high depth perception of ''Tyrannosaurus'' may have been due to the prey it had to hunt, noting that it had to hunt horned dinosaurs such as ''Triceratops'', armored dinosaurs such as ''Ankylosaurus
''Ankylosaurus'' is a genus of armored dinosaur. Its fossils have been found in geological formations dating to the very end of the Cretaceous Period, about 68–66 million years ago, in western North America, making it among the last of the n ...
'', and the duck-billed dinosaurs and their possibly complex social behaviors. He would suggest that this made precision more crucial for ''Tyrannosaurus'' enabling it to, "get in, get that blow in and take it down." In contrast, '' Acrocanthosaurus'' had limited depth perception because they hunted large sauropods, which were relatively rare during the time of ''Tyrannosaurus''.
''Tyrannosaurus'' had very large olfactory bulb
The olfactory bulb (Latin: ''bulbus olfactorius'') is a grey matter, neural structure of the vertebrate forebrain involved in olfaction, the sense of odor, smell. It sends olfactory information to be further processed in the amygdala, the orbitof ...
s and olfactory nerve
The olfactory nerve, also known as the first cranial nerve, cranial nerve I, or simply CN I, is a cranial nerve that contains sensory nerve fibers relating to the sense of smell.
The afferent nerve fibers of the olfactory receptor neurons tr ...
s relative to their brain size, the organs responsible for a heightened sense of smell. This suggests that the sense of smell was highly developed, and implies that tyrannosaurs could detect carcasses by scent alone across great distances. The sense of smell in tyrannosaurs may have been comparable to modern vulture
A vulture is a bird of prey that scavenges on carrion. There are 23 extant species of vulture (including Condors). Old World vultures include 16 living species native to Europe, Africa, and Asia; New World vultures are restricted to North and ...
s, which use scent to track carcasses for scavenging. Research on the olfactory bulbs has shown that ''T. rex'' had the most highly developed sense of smell of 21 sampled non-avian dinosaur species.
Somewhat unusually among theropods, ''T. rex'' had a very long cochlea
The cochlea is the part of the inner ear involved in hearing. It is a spiral-shaped cavity in the bony labyrinth, in humans making 2.75 turns around its axis, the modiolus. A core component of the cochlea is the Organ of Corti, the sensory org ...
. The length of the cochlea is often related to hearing acuity, or at least the importance of hearing in behavior, implying that hearing was a particularly important sense to tyrannosaurs. Specifically, data suggests that ''T. rex'' heard best in the low-frequency range, and that low-frequency sounds were an important part of tyrannosaur behavior. A 2017 study by Thomas Carr and colleagues found that the snout of tyrannosaurids was highly sensitive, based on a high number of small openings in the facial bones of the related ''Daspletosaurus'' that contained sensory neuron
Sensory neurons, also known as afferent neurons, are neurons in the nervous system, that convert a specific type of stimulus, via their receptors, into action potentials or graded potentials. This process is called sensory transduction. The cell ...
s. The study speculated that tyrannosaurs might have used their sensitive snouts to measure the temperature of their nests and to gently pick up eggs and hatchlings, as seen in modern crocodylians.
Another study published in 2021 further suggests that ''Tyrannosaurus'' had an acute sense of touch, based on neurovascular canals in the front of its jaws, which it could utilize to better detect and consume prey. The study, published by Kawabe and Hittori ''et al.,'' suggests that ''Tyrannosaurus'' could also accurately sense slight differences in material and movement, allowing it to utilize different feeding strategies on different parts of its prey's carcasses depending on the situation. The sensitive neurovascular canals of ''Tyrannosaurus'' also likely were adapted to performing fine movements and behaviors such as nest building, parental care, and other social behavior such as intraspecific communication. The results of this study also align with results made in studying the related tyrannosaurid ''Daspletosaurus horneri
''Daspletosaurus'' ( ; meaning "frightful lizard") is a genus of tyrannosaurid dinosaur that lived in Laramidia between about 79.5 and 74 million years ago, during the Late Cretaceous Period. The genus ''Daspletosaurus'' contains three species ...
'' and the allosauroid ''Neovenator
''Neovenator'' (nee-o-ven-a-tor meaning "new hunter") is a genus of carcharodontosaurian theropod dinosaur. It is known from several skeletons found in the Early Cretaceous (Barremian~130-125 million years ago) Wessex Formation on the south coa ...
'', which have similar neurovascular adaptations, suggesting that the faces of theropods were highly sensitive to pressure and touch. However, a more recent study reviewing the evolution of the trigeminal canals among sauropsids notes that a much denser network of neurovascular canals in the snout and lower jaw is more commonly encountered in aquatic or semiaquatic taxa (e.g., '' Spinosaurus'', ''Halszkaraptor
''Halszkaraptor'' (; meaning " Halszka's seizer") is a genus of waterfowl-like dromaeosaurid dinosaurs from Mongolia that lived during the Late Cretaceous period. It contains only one known species, ''Halszkaraptor escuilliei''.
The type speci ...
'', '' Plesiosaurus''), and taxa that developed a rhamphotheca (e.g., ''Caenagnathasia
''Caenagnathasia'' ('recent jaw from Asia') is a small caenagnathid oviraptorosaurian theropod from the Late Cretaceous of Uzbekistan.
Discovery
The type species ''Caenagnathasia martinsoni'' was named and described in 1994 by Philip J. Currie ...
''), while the network of canals in ''Tyrannosaurus'' appears simpler, though still more derived than in most ornithischians, and overall
terrestrial taxa such as tyrannosaurids and ''Neovenator'' may have had average facial sensitivity for non-edentulous terrestrial theropods, although further research is needed. The neurovascular canals in ''Tyrannosaurus'' may instead have supported soft tissue structures for thermoregulation or social signaling, the latter of which could be confirmed by the fact that the neurovascular network of canals may have changed during ontogeny.
A study by Grant R. Hurlburt, Ryan C. Ridgely and Lawrence Witmer obtained estimates for Encephalization Quotients (EQs), based on reptiles and birds, as well as estimates for the ratio of cerebrum to brain mass. The study concluded that ''Tyrannosaurus'' had the relatively largest brain of all adult non-avian dinosaurs with the exception of certain small maniraptoriforms (''Bambiraptor
''Bambiraptor'' is a Late Cretaceous, 72-million-year-old, bird-like dromaeosaurid theropod dinosaur described by scientists at the University of Kansas, Yale University, and the University of New Orleans.
The holotype fossil is less than one m ...
'', '' Troodon'' and ''Ornithomimus
''Ornithomimus'' (; "bird mimic") is a genus of ornithomimid dinosaurs from the Late Cretaceous Period of what is now North America. ''Ornithomimus'' was a swift bipedal theropod which fossil evidence indicates was covered in feathers, equipped w ...
''). The study found that ''Tyrannosauruss relative brain size was still within the range of modern reptiles, being at most 2 standard deviations above the mean of non-avian reptile EQs. The estimates for the ratio of cerebrum mass to brain mass would range from 47.5 to 49.53 percent. According to the study, this is more than the lowest estimates for extant birds (44.6 percent), but still close to the typical ratios of the smallest sexually mature alligators which range from 45.9–47.9 percent. Other studies, such as those by Steve Brusatte, indicate the encephalization quotient of ''Tyrannosaurus'' was similar in range (2.0–2.4) to a chimpanzee
The chimpanzee (''Pan troglodytes''), also known as simply the chimp, is a species of great ape native to the forest and savannah of tropical Africa. It has four confirmed subspecies and a fifth proposed subspecies. When its close relative th ...
(2.2–2.5), though this may be debatable as reptilian and mammalian encephalization quotients are not equivalent.
Social behavior
Philip J. Currie
Philip John Currie (born March 13, 1949) is a Canadian palaeontologist and museum curator who helped found the Royal Tyrrell Museum of Palaeontology in Drumheller, Alberta and is now a professor at the University of Alberta in Edmonton. In the ...
suggested that Tyrannosaurus may have been pack hunters, comparing ''T. rex'' to related species ''Tarbosaurus bataar
''Tarbosaurus'' ( ; meaning "alarming lizard") is a genus of tyrannosaurid dinosaur that flourished in Asia about 70 million years ago, at the end of the Late Cretaceous Period, considered to contain a single known species, ''Tarbosaurus bataa ...
'' and ''Albertosaurus sarcophagus
''Albertosaurus'' (; meaning "Alberta lizard") is a genus of tyrannosaurid theropod dinosaurs that lived in western North America during the Late Cretaceous Period, about 71 million years ago. The type species, ''A. sarcophagus'', was app ...
'', citing fossil evidence that may indicate gregarious
Sociality is the degree to which individuals in an animal population tend to associate in social groups (gregariousness) and form cooperative societies.
Sociality is a survival response to evolutionary pressures. For example, when a mother wasp ...
(describing animals that travel in herds or packs) behavior. A find in South Dakota
South Dakota (; Sioux language, Sioux: , ) is a U.S. state in the West North Central states, North Central region of the United States. It is also part of the Great Plains. South Dakota is named after the Lakota people, Lakota and Dakota peo ...
where three ''T. rex'' skeletons were in close proximity may suggest the formation of a pack. Cooperative pack hunting may have been an effective strategy for subduing prey with advanced anti-predator adaptations which pose potential lethality such as ''Triceratops
''Triceratops'' ( ; ) is a genus of herbivore, herbivorous Chasmosaurinae, chasmosaurine Ceratopsidae, ceratopsid dinosaur that first appeared during the late Maastrichtian stage of the Late Cretaceous Period (geology), period, about 68 m ...
'' and ''Ankylosaurus
''Ankylosaurus'' is a genus of armored dinosaur. Its fossils have been found in geological formations dating to the very end of the Cretaceous Period, about 68–66 million years ago, in western North America, making it among the last of the n ...
''.
Currie's pack-hunting ''T. rex'' hypothesis has been criticized for not having been peer-review
Peer review is the evaluation of work by one or more people with similar competencies as the producers of the work (peers). It functions as a form of self-regulation by qualified members of a profession within the relevant field. Peer review ...
ed, but rather was discussed in a television interview and book called ''Dino Gangs''. The Currie theory for pack hunting by ''T. rex'' is based mainly by analogy to a different species, ''Tarbosaurus bataar''. Evidence of gregariousness in ''T. bataar'' itself has not been peer-reviewed, and to Currie's own admission, can only be interpreted with reference to evidence in other closely related species. According to Currie gregariousness in ''Albertosaurus sarcophagus'' is supported by the discovery of 26 individuals with varied ages in the Dry Island bonebed. He ruled out the possibility of a predator trap due to the similar preservation state of individuals and the near absence of herbivores.[ (not printed until 2000)]
Additional support of Tyrannosaurid gregariousness can be found in fossilized trackways from the Upper Cretaceous Wapiti Formation
The Wapiti Formation is a geological formation of the Western Canada Sedimentary Basin in northwestern Alberta, and northeastern British Columbia, Canada. Its deposition spanned the time interval from the lower Campanian through to the upper Maast ...
of northeastern British Columbia
British Columbia (commonly abbreviated as BC) is the westernmost province of Canada, situated between the Pacific Ocean and the Rocky Mountains. It has a diverse geography, with rugged landscapes that include rocky coastlines, sandy beaches, ...
, Canada, left by three tyrannosaurids traveling in the same direction. According to scientists assessing the Dino Gangs program, the evidence for pack hunting in ''Tarbosaurus'' and ''Albertosaurus'' is weak and based on group skeletal remains for which alternate explanations may apply (such as drought or a flood forcing dinosaurs to die together in one place). Others researchers have speculated that instead of large theropod social groups, some of these finds represent behavior more akin to Komodo dragon
The Komodo dragon (''Varanus komodoensis''), also known as the Komodo monitor, is a member of the monitor lizard family Varanidae that is endemic to the Indonesian islands of Komodo, Rinca, Flores, and Gili Motang. It is the largest extant ...
-like mobbing of carcasses, even going as far as to say true pack-hunting behavior may not exist in any non-avian dinosaurs due to its rarity in modern predators.
Evidence of intraspecific attack was found by Joseph Peterson and his colleagues in the juvenile ''Tyrannosaurus'' nicknamed Jane
Jane may refer to:
* Jane (given name), a feminine given name
* Jane (surname), related to the given name
Film and television
* ''Jane'' (1915 film), a silent comedy film directed by Frank Lloyd
* ''Jane'' (2016 film), a South Korean drama fil ...
. Peterson and his team found that Jane's skull showed healed puncture wounds on the upper jaw and snout which they believe came from another juvenile ''Tyrannosaurus''. Subsequent CT scans of Jane's skull would further confirm the team's hypothesis, showing that the puncture wounds came from a traumatic injury and that there was subsequent healing. The team would also state that Jane's injuries were structurally different from the parasite-induced lesions found in Sue and that Jane's injuries were on her face whereas the parasite that infected Sue caused lesions to the lower jaw.
Feeding strategies
Most paleontologists accept that ''Tyrannosaurus'' was both an active predator
Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill th ...
and a scavenger
Scavengers are animals that consume dead organisms that have died from causes other than predation or have been killed by other predators. While scavenging generally refers to carnivores feeding on carrion, it is also a herbivorous feeding b ...
like most large carnivores. By far the largest carnivore in its environment, ''T. rex'' was most likely an apex predator, preying upon hadrosaur
Hadrosaurids (), or duck-billed dinosaurs, are members of the ornithischian family Hadrosauridae. This group is known as the duck-billed dinosaurs for the flat duck-bill appearance of the bones in their snouts. The ornithopod family, which includ ...
s, armored herbivores like ceratopsia
Ceratopsia or Ceratopia ( or ; Greek: "horned faces") is a group of herbivorous, beaked dinosaurs that thrived in what are now North America, Europe, and Asia, during the Cretaceous Period, although ancestral forms lived earlier, in the Jurassic. ...
ns and ankylosaur
Ankylosauria is a group of herbivorous dinosaurs of the order Ornithischia. It includes the great majority of dinosaurs with armor in the form of bony osteoderms, similar to turtles. Ankylosaurs were bulky quadrupeds, with short, powerful limbs. ...
s, and possibly sauropod
Sauropoda (), whose members are known as sauropods (; from '' sauro-'' + '' -pod'', 'lizard-footed'), is a clade of saurischian ('lizard-hipped') dinosaurs. Sauropods had very long necks, long tails, small heads (relative to the rest of their bo ...
s. A study in 2012 by Karl Bates and Peter Falkingham found that ''Tyrannosaurus'' had the most powerful bite of any terrestrial animal that has ever lived, finding an adult ''Tyrannosaurus'' could have exerted 35,000 to 57,000 N (7,868 to 12,814 lbf
The pound of force or pound-force (symbol: lbf, sometimes lbf,) is a unit of force used in some systems of measurement, including English Engineering units and the foot–pound–second system.
Pound-force should not be confused with pound-m ...
) of force in the back teeth. Even higher estimates were made by Mason B. Meers in 2003. This allowed it to crush bones during repetitive biting and fully consume the carcasses of large dinosaurs. Stephan Lautenschlager and colleagues calculated that ''Tyrannosaurus'' was capable of a maximum jaw gape of around 80 degrees, a necessary adaptation for a wide range of jaw angles to power the creature's strong bite.
A debate exists, however, about whether ''Tyrannosaurus'' was primarily a predator
Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill th ...
or a pure scavenger
Scavengers are animals that consume dead organisms that have died from causes other than predation or have been killed by other predators. While scavenging generally refers to carnivores feeding on carrion, it is also a herbivorous feeding b ...
. The debate originated in a 1917 study by Lambe which argued that large theropods were pure scavengers because ''Gorgosaurus'' teeth showed hardly any wear. This argument disregarded the fact that theropods replaced their teeth quite rapidly. Ever since the first discovery of ''Tyrannosaurus'' most scientists have speculated that it was a predator; like modern large predators it would readily scavenge or steal another predator's kill if it had the opportunity.
Paleontologist Jack Horner Jack Horner may refer to:
*''Little Jack Horner'', a nursery rhyme
People
* Jack Horner (baseball) (1863–1910), American professional baseball player
*Jack Horner (journalist) (1912–2005), Gordon John Horner, Minnesota sportscaster
* Jack B. H ...
has been a major proponent of the view that ''Tyrannosaurus'' was not a predator at all but instead was exclusively a scavenger. He has put forward arguments in the popular literature to support the pure scavenger hypothesis:
* Tyrannosaur arms are short when compared to other known predators. Horner argues that the arms were too short to make the necessary gripping force to hold on to prey. Other paleontologists such as Thomas Holtz Jr. argued that there are plenty of modern-day predators that do not use their forelimbs to hunt such as wolves
The wolf (''Canis lupus''; plural, : wolves), also known as the gray wolf or grey wolf, is a large Canis, canine native to Eurasia and North America. More than thirty subspecies of Canis lupus, subspecies of ''Canis lupus'' have been reco ...
, hyena
Hyenas, or hyaenas (from Ancient Greek , ), are feliform carnivoran mammals of the family Hyaenidae . With only four extant species (each in its own genus), it is the fifth-smallest family in the Carnivora and one of the smallest in the clas ...
s, and secretary birds as well as other extinct animals thought to be predators that would not have used their forelimbs such as Phorusrhacids.
* Tyrannosaurs had large olfactory bulb
The olfactory bulb (Latin: ''bulbus olfactorius'') is a grey matter, neural structure of the vertebrate forebrain involved in olfaction, the sense of odor, smell. It sends olfactory information to be further processed in the amygdala, the orbitof ...
s and olfactory nerve
The olfactory nerve, also known as the first cranial nerve, cranial nerve I, or simply CN I, is a cranial nerve that contains sensory nerve fibers relating to the sense of smell.
The afferent nerve fibers of the olfactory receptor neurons tr ...
s (relative to their brain size). These suggest a highly developed sense of smell which could sniff out carcasses over great distances, as modern vulture
A vulture is a bird of prey that scavenges on carrion. There are 23 extant species of vulture (including Condors). Old World vultures include 16 living species native to Europe, Africa, and Asia; New World vultures are restricted to North and ...
s do. Research on the olfactory bulbs of dinosaurs has shown that ''Tyrannosaurus'' had the most highly developed sense of smell of 21 sampled dinosaurs.
* Tyrannosaur teeth could crush bone, and therefore could extract as much food (bone marrow
Bone marrow is a semi-solid tissue found within the spongy (also known as cancellous) portions of bones. In birds and mammals, bone marrow is the primary site of new blood cell production (or haematopoiesis). It is composed of hematopoietic ce ...
) as possible from carcass remnants, usually the least nutritious parts. Karen Chin and colleagues have found bone fragments in coprolite
A coprolite (also known as a coprolith) is fossilized feces. Coprolites are classified as trace fossils as opposed to body fossils, as they give evidence for the animal's behaviour (in this case, diet) rather than morphology. The name is de ...
s (fossilized feces) that they attribute to tyrannosaurs, but point out that a tyrannosaur's teeth were not well adapted to systematically chewing bone like hyena
Hyenas, or hyaenas (from Ancient Greek , ), are feliform carnivoran mammals of the family Hyaenidae . With only four extant species (each in its own genus), it is the fifth-smallest family in the Carnivora and one of the smallest in the clas ...
s do to extract marrow.[ Summary at ]
* Since at least some of ''Tyrannosaurus''s potential prey could move quickly, evidence that it walked instead of ran could indicate that it was a scavenger. On the other hand, recent analyses suggest that ''Tyrannosaurus'', while slower than large modern terrestrial predators, may well have been fast enough to prey on large hadrosaurs and ceratopsians.
Other evidence suggests hunting behavior in ''Tyrannosaurus''. The eye sockets of tyrannosaurs are positioned so that the eyes would point forward, giving them binocular vision slightly better than that of modern hawk
Hawks are bird of prey, birds of prey of the family Accipitridae. They are widely distributed and are found on all continents except Antarctica.
* The subfamily Accipitrinae includes goshawks, sparrowhawks, sharp-shinned hawks and others. Th ...
s. It is not obvious why natural selection
Natural selection is the differential survival and reproduction of individuals due to differences in phenotype. It is a key mechanism of evolution, the change in the heritable traits characteristic of a population over generations. Charle ...
would have favored this long-term trend if tyrannosaurs had been pure scavengers, which would not have needed the advanced depth perception
Depth perception is the ability to perceive distance to objects in the world using the visual system and visual perception. It is a major factor in perceiving the world in three dimensions. Depth perception happens primarily due to stereopsis an ...
that stereoscopic vision provides. In modern animals, binocular vision is found mainly in predators.
A 2021 study focused on the vision and hearing of the small theropod ''Shuvuuia
''Shuvuuia'' is a genus of bird-like theropod dinosaur from the late Cretaceous period of Mongolia. It is a member of the family Alvarezsauridae, small coelurosaurian dinosaurs which are characterized by short but powerful forelimbs specialized f ...
'', to which ''Tyrannosaurus'' was compared suggests that ''Tyrannosaurus'' was diurnal and would have hunted predominantly during daylight hours, a feature it shared with ''Dromaeosaurus
''Dromaeosaurus'' (, "running lizard") is a genus of dromaeosaurid theropod dinosaur which lived during the Late Cretaceous period (middle late Campanian and Maastrichtian), sometime between 80 and 69 million years ago, in Alberta, Canada and the ...
'', a third dinosaur compared to ''Shuvuuia'' in the study.
A skeleton of the hadrosaurid ''Edmontosaurus
''Edmontosaurus'' ( ) (meaning "lizard from Edmonton") is a genus of hadrosaurid (duck-billed) dinosaur. It contains two known species: ''Edmontosaurus regalis'' and ''Edmontosaurus annectens''. Fossils of ''E. regalis'' have been found in rocks ...
annectens'' has been described from Montana with healed tyrannosaur-inflicted damage on its tail vertebra
The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic ...
e. The fact that the damage seems to have healed suggests that the ''Edmontosaurus'' survived a tyrannosaur's attack on a living target, i.e. the tyrannosaur had attempted active predation. Despite the consensus that the tail bites were caused by ''Tyrannosaurus'', there has been some evidence to show that they might have been created by other factors. For example, a 2014 study suggested that the tail injuries might have been due to ''Edmontosaurus'' individuals stepping on each other, while another study in 2020 backs up the hypothesis that biomechanical stress is the cause for the tail injuries. There is also evidence for an aggressive interaction between a ''Triceratops
''Triceratops'' ( ; ) is a genus of herbivore, herbivorous Chasmosaurinae, chasmosaurine Ceratopsidae, ceratopsid dinosaur that first appeared during the late Maastrichtian stage of the Late Cretaceous Period (geology), period, about 68 m ...
'' and a ''Tyrannosaurus'' in the form of partially healed tyrannosaur tooth marks on a ''Triceratops'' brow horn and squamosal (a bone of the neck frill); the bitten horn is also broken, with new bone growth after the break. It is not known what the exact nature of the interaction was, though: either animal could have been the aggressor. Since the ''Triceratops'' wounds healed, it is most likely that the ''Triceratops'' survived the encounter and managed to overcome the ''Tyrannosaurus''. In a battle against a bull ''Triceratops'', the ''Triceratops'' would likely defend itself by inflicting fatal wounds to the ''Tyrannosaurus'' using its sharp horns. Studies of Sue found a broken and healed fibula
The fibula or calf bone is a leg bone on the lateral side of the tibia, to which it is connected above and below. It is the smaller of the two bones and, in proportion to its length, the most slender of all the long bones. Its upper extremity is ...
and tail vertebrae, scarred facial bones and a tooth from another ''Tyrannosaurus'' embedded in a neck vertebra, providing evidence for aggressive behavior. Studies on hadrosaur vertebrae from the Hell Creek Formation that were punctured by the teeth of what appears to be a late-stage juvenile ''Tyrannosaurus'' indicate that despite lacking the bone-crushing adaptations of the adults, young individuals were still capable of using the same bone-puncturing feeding technique as their adult counterparts.
''Tyrannosaurus'' may have had infectious saliva
Saliva (commonly referred to as spit) is an extracellular fluid produced and secreted by salivary glands in the mouth. In humans, saliva is around 99% water, plus electrolytes, mucus, white blood cells, epithelial cells (from which DNA can be ...
used to kill its prey, as proposed by William Abler
William L. Abler or simply known as Bill Abler was a paleontologist who has mostly studied the teeth of dinosaurs and also proposed a radical theory of human language that sees it sharing the same fundamental principles as mathematics and algebra ...
in 1992. Abler observed that the (tiny protuberances) on the cutting edges of the teeth are closely spaced, enclosing little chambers. These chambers might have trapped pieces of carcass with bacteria, giving ''Tyrannosaurus'' a deadly, infectious bite much like the Komodo dragon
The Komodo dragon (''Varanus komodoensis''), also known as the Komodo monitor, is a member of the monitor lizard family Varanidae that is endemic to the Indonesian islands of Komodo, Rinca, Flores, and Gili Motang. It is the largest extant ...
was thought to have. Jack Horner and Don Lessem, in a 1993 popular book, questioned Abler's hypothesis, arguing that ''Tyrannosaurus''s tooth serrations as more like cubes in shape than the serrations on a Komodo monitor's teeth, which are rounded.
''Tyrannosaurus'', and most other theropods, probably primarily processed carcasses with lateral shakes of the head, like crocodilians. The head was not as maneuverable as the skulls of allosauroids, due to flat joints of the neck vertebrae.
Cannibalism
Evidence also strongly suggests that tyrannosaurs were at least occasionally cannibalistic. ''Tyrannosaurus'' itself has strong evidence pointing towards it having been cannibalistic in at least a scavenging capacity based on tooth marks on the foot bones, humerus, and metatarsals of one specimen. Fossils from the Fruitland Formation, Kirtland Formation (both Campanian in age) and the Maastrichtian aged Ojo Alamo Formation
The Ojo Alamo Formation is a geologic formation in New Mexico spanning the Mesozoic/Cenozoic boundary. Non-avian dinosaur fossils have controversially been identified in beds of this formation dating from after the Cretaceous–Paleogene extinctio ...
suggest that cannibalism was present in various tyrannosaurid genera of the San Juan Basin. The evidence gathered from the specimens suggests opportunistic feeding behavior in tyrannosaurids that cannibalized members of their own species. A study from Currie, Horner, Erickson and Longrich in 2010 has been put forward as evidence of cannibalism in the genus ''Tyrannosaurus''.[ They studied some ''Tyrannosaurus'' specimens with tooth marks in the bones, attributable to the same genus. The tooth marks were identified in the ]humerus
The humerus (; ) is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius and ulna, and consists of three sections. The humeral upper extremity consists of a roun ...
, foot bones and metatarsals, and this was seen as evidence for opportunistic scavenging, rather than wounds caused by intraspecific combat. In a fight, they proposed it would be difficult to reach down to bite in the feet of a rival, making it more likely that the bitemarks were made in a carcass. As the bitemarks were made in body parts with relatively scantly amounts of flesh, it is suggested that the ''Tyrannosaurus'' was feeding on a cadaver in which the more fleshy parts already had been consumed. They were also open to the possibility that other tyrannosaurids
Tyrannosauridae (or tyrannosaurids, meaning "tyrant lizards") is a family (biology), family of coelurosaurian Theropoda, theropod dinosaurs that comprises two subfamilies containing up to thirteen genus, genera, including the eponymous ''Tyrannos ...
practiced cannibalism.
Parenting
While there is no direct evidence of ''Tyrannosaurus'' raising their young (the rarity of juvenile and nest Tyrannosaur fossils has left researchers guessing), it has been suggested by some that like its closest living relatives, modern archosaurs (birds and crocodiles) ''Tyrannosaurus'' may have protected and fed its young. Crocodilians and birds are often suggested by some paleontologists to be modern analogues for dinosaur parenting. Direct evidence of parental behavior exists in other dinosaurs such as '' Maiasaura peeblesorum'', the first dinosaur to have been discovered to raise its young, as well as more closely related Oviraptorids, the latter suggesting parental behavior in theropods.
Pathology
In 2001, Bruce Rothschild and others published a study examining evidence for stress fractures and tendon avulsions
An avulsion fracture is a bone fracture which occurs when a fragment of bone tears away from the main mass of bone as a result of physical trauma. This can occur at the ligament by the application of forces external to the body (such as a fa ...
in theropod dinosaurs and the implications for their behavior. Since stress fractures are caused by repeated trauma rather than singular events they are more likely to be caused by regular behavior than other types of injuries. Of the 81 ''Tyrannosaurus'' foot bones examined in the study, one was found to have a stress fracture, while none of the 10 hand bones were found to have stress fractures. The researchers found tendon avulsions only among ''Tyrannosaurus'' and '' Allosaurus''. An avulsion injury left a divot on the humerus of Sue the ''T. rex'', apparently located at the origin of the deltoid Deltoid (delta-shaped) can refer to:
* The deltoid muscle, a muscle in the shoulder
* Kite (geometry), also known as a deltoid, a type of quadrilateral
* A deltoid curve, a three-cusped hypocycloid
* A leaf shape
* The deltoid tuberosity, a part of ...
or teres major muscles. The presence of avulsion injuries being limited to the forelimb and shoulder in both ''Tyrannosaurus'' and ''Allosaurus'' suggests that theropods may have had a musculature more complex than and functionally different from those of birds. The researchers concluded that Sue's tendon avulsion was probably obtained from struggling prey. The presence of stress fractures and tendon avulsions, in general, provides evidence for a "very active" predation-based diet rather than obligate scavenging.
A 2009 study showed that smooth-edged holes in the skulls of several specimens might have been caused by ''Trichomonas
''Trichomonas'' is a genus of anaerobic excavate parasites of vertebrates. It was first discovered by Alfred François Donné in 1836 when he found these parasites in the pus of a patient suffering from vaginitis, an inflammation of the vagina. ...
''-like parasites that commonly infect bird
Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweigh ...
s. According to the study, seriously infected individuals, including "Sue" and MOR 980 ("Peck's Rex"), might therefore have died from starvation after feeding became increasingly difficult. Previously, these holes had been explained by the bacterious bone infection Actinomycosis or by intraspecific attacks. A subsequent study found that while trichomoniasis has many attributes of the model proposed (osteolytic, intra oral) several features make the assumption that it was the cause of death less supportable by evidence. For example, the observed sharp margins with little reactive bone shown by the radiographs of ''Trichomonas''-infected birds are dissimilar to the reactive bone seen in the affected ''T. rex'' specimens. Also, trichomoniasis can be very rapidly fatal in birds (14 days or less) albeit in its milder form, and this suggests that if a ''Trichomonas''-like protozoan is the culprit, trichomoniasis was less acute in its non-avian dinosaur form during the Late Cretaceous. Finally, the relative size of this type of lesions is much larger in small bird throats, and may not have been enough to choke a ''T. rex''. A more recent study examining the pathologies concluded that the osseous alteration observed most closely resembles those around healing human cranial trepanations and healing fractures in the Triassic reptile '' Stagonolepis,'' in the absence of infection. The possible cause may instead have been intraspecific combat.
One study of ''Tyrannosaurus'' specimens with tooth marks in the bones attributable to the same genus was presented as evidence of cannibalism
Cannibalism is the act of consuming another individual of the same species as food. Cannibalism is a common ecological interaction in the animal kingdom and has been recorded in more than 1,500 species. Human cannibalism is well documented, b ...
. Tooth marks in the humerus
The humerus (; ) is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius and ulna, and consists of three sections. The humeral upper extremity consists of a roun ...
, foot bones and metatarsals, may indicate opportunistic scavenging, rather than wounds caused by combat with another ''T. rex''. Other tyrannosaurids
Tyrannosauridae (or tyrannosaurids, meaning "tyrant lizards") is a family (biology), family of coelurosaurian Theropoda, theropod dinosaurs that comprises two subfamilies containing up to thirteen genus, genera, including the eponymous ''Tyrannos ...
may also have practiced cannibalism.
Paleoecology
''Tyrannosaurus'' lived during what is referred to as the Lancian
The Lancian was a North American faunal stage of the Late Cretaceous. It was the final stage of the Cretaceous period in North America, lasting from approximately 70.6 to 66 million years ago.
Geology
Terrestrial sedimentary strata from the Judit ...
faunal stage (Maastrichtian
The Maastrichtian () is, in the ICS geologic timescale, the latest age (uppermost stage) of the Late Cretaceous Epoch or Upper Cretaceous Series, the Cretaceous Period or System, and of the Mesozoic Era or Erathem. It spanned the interval from ...
age) at the end of the Late Cretaceous. ''Tyrannosaurus'' ranged from Canada
Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by tot ...
in the north to at least New Mexico in the south of Laramidia. During this time ''Triceratops
''Triceratops'' ( ; ) is a genus of herbivore, herbivorous Chasmosaurinae, chasmosaurine Ceratopsidae, ceratopsid dinosaur that first appeared during the late Maastrichtian stage of the Late Cretaceous Period (geology), period, about 68 m ...
'' was the major herbivore in the northern portion of its range, while the titanosaurian
Titanosaurs (or titanosaurians; members of the group Titanosauria) were a diverse group of sauropod dinosaurs, including genera from all seven continents. The titanosaurs were the last surviving group of long-necked sauropods, with taxa still thr ...
sauropod
Sauropoda (), whose members are known as sauropods (; from '' sauro-'' + '' -pod'', 'lizard-footed'), is a clade of saurischian ('lizard-hipped') dinosaurs. Sauropods had very long necks, long tails, small heads (relative to the rest of their bo ...
''Alamosaurus
''Alamosaurus'' (; meaning "Ojo Alamo lizard") is a genus of opisthocoelicaudiine titanosaurian sauropod dinosaurs, containing a single known species, ''Alamosaurus sanjuanensis'', from the late Cretaceous Period of what is now southern North Am ...
'' "dominated" its southern range. ''Tyrannosaurus'' remains have been discovered in different ecosystems, including inland and coastal subtropical, and semi-arid plains.
Several notable ''Tyrannosaurus'' remains have been found in the Hell Creek Formation. During the Maastrichtian this area was subtropical
The subtropical zones or subtropics are geographical zone, geographical and Köppen climate classification, climate zones to the Northern Hemisphere, north and Southern Hemisphere, south of the tropics. Geographically part of the Geographical z ...
, with a warm and humid climate. The flora consisted mostly of angiosperms
Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (), commonly called angiosperms. The term "angiosperm" is derived from the Greek words ('container, vessel') and ('seed'), and refers to those plants th ...
, but also included trees like dawn redwood (''Metasequoia
''Metasequoia'', or dawn redwoods, is a genus of fast-growing deciduous trees, one of three species of pinophyta, conifers known as redwoods. The living species ''Metasequoia glyptostroboides'' is native to Lichuan, Hubei, Lichuan county in Hube ...
'') and ''Araucaria
''Araucaria'' (; original pronunciation: .ɾawˈka. ɾja is a genus of evergreen Conifer, coniferous trees in the family Araucariaceae. There are 20 extant taxon, extant species in New Caledonia (where 14 species are endemism, ende ...
''. ''Tyrannosaurus'' shared this ecosystem with ceratopsia
Ceratopsia or Ceratopia ( or ; Greek: "horned faces") is a group of herbivorous, beaked dinosaurs that thrived in what are now North America, Europe, and Asia, during the Cretaceous Period, although ancestral forms lived earlier, in the Jurassic. ...
ns '' Leptoceratops'', ''Torosaurus
''Torosaurus'' ("perforated lizard", in reference to the large openings in its frill) is a genus of herbivorous ceratopsid dinosaur that lived during the late Maastrichtian stage of the Cretaceous period, between 68 and 66 million years ago, tho ...
'', and ''Triceratops'', the hadrosaurid ''Edmontosaurus annectens
''Edmontosaurus annectens'' (meaning "connected lizard from Edmonton") is a species of flat-headed and duck-billed (hadrosaurid) dinosaur from the very end of the Cretaceous Period (geology), Period, in what is now North America. Remains of ''E. ...
,'' the parksosaurid '' Thescelosaurus'', the ankylosaur
Ankylosauria is a group of herbivorous dinosaurs of the order Ornithischia. It includes the great majority of dinosaurs with armor in the form of bony osteoderms, similar to turtles. Ankylosaurs were bulky quadrupeds, with short, powerful limbs. ...
s ''Ankylosaurus
''Ankylosaurus'' is a genus of armored dinosaur. Its fossils have been found in geological formations dating to the very end of the Cretaceous Period, about 68–66 million years ago, in western North America, making it among the last of the n ...
'' and '' Denversaurus'', the pachycephalosaur
Pachycephalosauria (; from Greek παχυκεφαλόσαυρος for 'thick headed lizards') is a clade of ornithischian dinosaurs. Along with Ceratopsia, it makes up the clade Marginocephalia. With the exception of two species, most pachyc ...
s ''Pachycephalosaurus
''Pachycephalosaurus'' (; meaning "thick-headed lizard", from Greek ''pachys-/'' "thick", ''kephale/'' "head" and ''sauros/'' "lizard") is a genus of pachycephalosaurid dinosaurs. The type species, ''P. wyomingensis'', is the only known species, ...
'' and '' Sphaerotholus'', and the theropods ''Ornithomimus
''Ornithomimus'' (; "bird mimic") is a genus of ornithomimid dinosaurs from the Late Cretaceous Period of what is now North America. ''Ornithomimus'' was a swift bipedal theropod which fossil evidence indicates was covered in feathers, equipped w ...
'', '' Struthiomimus'', '' Acheroraptor'', ''Dakotaraptor
''Dakotaraptor'' (meaning “thief from Dakota”) is a potentially chimaeric genus of large dromaeosaurid theropod dinosaur that lived in North America during the Late Cretaceous period. The remains have been found in the Maastrichtian stage of ...
'', ''Pectinodon
''Pectinodon'' is a genus of troodontid dinosaurs from the Late Cretaceous period (66 mya). It currently contains a single valid species, ''Pectinodon bakkeri'' (sometimes classified as ''Troodon bakkeri''), known only from teeth.
In 1982, ...
'' and ''Anzu Anzu may refer to:
*Anzû, a divine storm-bird in several Mesopotamian religions
* ''Anzu'' (dinosaur), a genus of theropod dinosaur containing the species ''Anzu wyliei''
As a given name
is a Japanese given name for females. Kyoko is an altern ...
''.
Another formation with ''Tyrannosaurus'' remains is the Lance Formation of Wyoming. This has been interpreted as a bayou
In usage in the Southern United States, a bayou () is a body of water typically found in a flat, low-lying area. It may refer to an extremely slow-moving stream, river (often with a poorly defined shoreline), marshy lake, wetland, or creek. They ...
environment similar to today's Gulf Coast. The fauna was very similar to Hell Creek, but with '' Struthiomimus'' replacing its relative ''Ornithomimus''. The small ceratopsian '' Leptoceratops'' also lived in the area.
In its southern range ''Tyrannosaurus'' lived alongside the titanosaur ''Alamosaurus'', the ceratopsians ''Torosaurus,'' ''Bravoceratops
''Bravoceratops'' is a genus of large chasmosaurine ceratopsid dinosaur that lived approximately 70 million years ago, and is known from the Late Cretaceous Javelina Formation in what is now Texas, United States.
Discovery and naming
''Bravocer ...
'' and ''Ojoceratops
''Ojoceratops'' ( meaning "Ojo Alamo horned face") is a genus of ceratopsian dinosaur which lived in what is now New Mexico, United States. ''Ojoceratops'' fossils have been recovered from strata of the Ojo Alamo Formation (Naashoibito Member), d ...
'', hadrosaurs which consisted of a species of ''Edmontosaurus, Kritosaurus
''Kritosaurus'' is an incompletely known genus of hadrosaurid (duck-billed) dinosaur. It lived about 74.5-66 million years ago, in the Late Cretaceous of North America. The name means "separated lizard" (referring to the arrangement of the cheek ...
'' and a possible species of ''Gryposaurus
''Gryposaurus'' (meaning "hooked-nosed (Ancient Greek, Greek ''grypos'') lizard"; sometimes incorrectly translated as "griffin (Latin ''gryphus'') lizard") was a genus of hadrosaur, duckbilled dinosaur that lived about 80 to 75 million years ...
'', the nodosaur ''Glyptodontopelta
''Glyptodontopelta'' (meaning "''Glyptodon'' shield") is a monospecific genus of nodosaurid dinosaur from New Mexico that lived during the Late Cretaceous (lower to upper Maastrichtian, 69 to 66 Ma) in what is now the Naashoibito member of the O ...
'', the oviraptorid ''Ojoraptosaurus'', possible species of the theropods '' Troodon'' and '' Richardoestesia'', and the pterosaur
Pterosaurs (; from Greek ''pteron'' and ''sauros'', meaning "wing lizard") is an extinct clade of flying reptiles in the order, Pterosauria. They existed during most of the Mesozoic: from the Late Triassic to the end of the Cretaceous (228 to ...
''Quetzalcoatlus
''Quetzalcoatlus'' is a genus of pterosaur known from the Late Cretaceous period of North America (Maastrichtian stage); its members were among the largest known flying animals of all time. ''Quetzalcoatlus'' is a member of the Azhdarchidae, ...
''. The region is thought to have been dominated by semi-arid inland plains, following the probable retreat of the Western Interior Seaway as global sea levels fell.
''Tyrannosaurus'' may have also inhabited Mexico's Lomas Coloradas formation in Sonora. Though skeletal evidence is lacking, six shed and broken teeth from the fossil bed have been thoroughly compared with other theropod genera and appear to be identical to those of ''Tyrannosaurus''. If true, the evidence indicates the range of ''Tyrannosaurus'' was possibly more extensive than previously believed. It is possible that tyrannosaurs were originally Asian species, migrating to North America before the end of the Cretaceous period.
Population estimates
According to studies published in 2021 by Charles Marshall ''et al.'', the total population of adult ''Tyrannosaurus'' at any given time was perhaps 20,000 individuals, with computer estimations also suggesting a total population no lower than 1,300 and no higher than 328,000. The authors themselves suggest that the estimate of 20,000 individuals is probably lower than what should be expected, especially when factoring in that disease pandemics could easily wipe out such a small population. Over the span of the genus' existence, it is estimated that there were about 127,000 generations and that this added up to a total of roughly 2.5 billion animals until their extinction.
In the same paper, it is suggested that in a population of ''Tyrannosaurus'' adults numbering 20,000, the number of individuals living in an area the size of California could be as high as 3,800 animals, while an area the size of Washington D.C. could support a population of only two adult ''Tyrannosaurus''. The study does not take into account the number of juvenile animals in the genus present in this population estimate due to their occupation of a different niche than the adults, and thus it is likely the total population was much higher when accounting for this factor. Simultaneously, studies of living carnivores suggest that some predator populations are higher in density than others of similar weight (such as jaguars and hyenas, which are similar in weight but have vastly differing population densities). Lastly, the study suggests that in most cases, only one in 80 million ''Tyrannosaurus'' would become fossilized, while the chances were likely as high as one in every 16,000 of an individual becoming fossilized in areas that had more dense populations.
Meiri (2022) questioned the reliability of the estimates, citing uncertainty in metabolic rate, body size, sex and age-specific survival rates, habitat requirements and range size variability as shortcomings Marshall ''et al.'' didn't take into account. The authors of the original publication replied that while they agree that their reported uncertainties were probably too small, their framework is flexible enough to accommodate uncerainty in physiology, and that their calculations do not depend on short-term changes in population density and geographic range, but rather on their long-term averages. Finally, they remark that they did estimate the range of reasonable survivorship curves and that they did include uncertainty in the time of onset of sexual maturity and in the growth curve by incorporating the
uncertainty in the maximum body mass.[ ]
Text was copied from this source, which is available under
Creative Commons Attribution 4.0 International License
Cultural significance
Since it was first described in 1905, ''T. rex'' has become the most widely recognized dinosaur species in popular culture
Popular culture (also called mass culture or pop culture) is generally recognized by members of a society as a set of practices, beliefs, artistic output (also known as, popular art or mass art) and objects that are dominant or prevalent in a ...
. It is the only dinosaur that is commonly known to the general public by its full scientific name (binomial name
In taxonomy, binomial nomenclature ("two-term naming system"), also called nomenclature ("two-name naming system") or binary nomenclature, is a formal system of naming species of living things by giving each a name composed of two parts, bot ...
) and the scientific abbreviation ''T. rex'' has also come into wide usage. Robert T. Bakker
Robert Thomas Bakker (born March 24, 1945) is an American paleontologist who helped reshape modern theories about dinosaurs, particularly by adding support to the theory that some dinosaurs were endothermic (warm-blooded). Along with his mentor J ...
notes this in ''The Dinosaur Heresies
''The Dinosaur Heresies: New Theories Unlocking the Mystery of the Dinosaurs and Their Extinction'' is a 1986 book written by Robert T. Bakker.
The book sums up the extant evidence that indicates that dinosaurs, rather than being Ectotherm, cold ...
'' and explains that, "a name like ''T. rex'' is just irresistible to the tongue."
See also
* History of paleontology
The history of paleontology traces the history of the effort to understand the history of life on Earth by studying the fossil record left behind by living organisms. Since it is concerned with understanding living organisms of the past, paleonto ...
* Sue (dinosaur)
Sue is the nickname given to FMNH PR 2081, which is one of the largest, most extensive, and best preserved ''Tyrannosaurus rex'' specimens ever found, at over 90 percent recovered by bulk. It was discovered on August 12, 1990, by American explo ...
(FMNH-PR-2081)
* Tyrannosauridae
Explanatory notes
References
Further reading
*
External links
The University of Edinburgh Lecture Dr Stephen Brusatte – Tyrannosaur Discoveries Feb 20, 2015
Stephen Brusatte Thomas Carr 2016
Exhibits
American Museum of Natural History
{{Featured article
1900s neologisms
Apex predators
Fossil taxa described in 1905
Hell Creek fauna
Lance fauna
Laramie Formation
Late Cretaceous dinosaurs of North America
Maastrichtian genus extinctions
Maastrichtian genus first appearances
Maastrichtian life
Paleontology in Colorado
Paleontology in Montana
Paleontology in South Dakota
Paleontology in Wyoming
Scollard fauna
Taxa named by Henry Fairfield Osborn
Tyrannosaurids